WRaster: Avoid undefined setjmp() behavior with libjpeg

Fix compiler warning:
load_jpeg.c: In function 'RLoadJPEG':
load_jpeg.c:100:17: warning: variable 'image' might be clobbered by 'longjmp' or 'vfork' [-Wclobbered]

As it was not working to only set the RImage *image as volatile,
I had to refactor the code by following the example from
libjpeg-turbo/libjpeg-turbo@410c028#diff-e7cb632359a2be17c1008b50f9ec85691cd5d66834d5fe8f63ef65ceb06682ee

wrlib/load_jpeg.c

@@ -95,97 +95,102 @@ static noreturn void my_error_exit(j_common_ptr cinfo)
 	longjmp(myerr->setjmp_buffer, 1);
 }
 
-RImage *RLoadJPEG(const char *file_name)
+static RImage *do_read_jpeg_file(struct jpeg_decompress_struct *cinfo, const char *file_name)
 {
 	RImage *image = NULL;
-	struct jpeg_decompress_struct cinfo;
 	int i;
 	unsigned char *ptr;
 	JSAMPROW buffer[1], bptr;
 	FILE *file;
-	/* We use our private extension JPEG error handler.
-	 * Note that this struct must live as long as the main JPEG parameter
-	 * struct, to avoid dangling-pointer problems.
-	 */
-	struct my_error_mgr jerr;
 
 	file = fopen(file_name, "rb");
 	if (!file) {
 		RErrorCode = RERR_OPEN;
 		return NULL;
 	}
 
-	cinfo.err = jpeg_std_error(&jerr.pub);
-	jerr.pub.error_exit = my_error_exit;
-	/* Establish the setjmp return context for my_error_exit to use. */
-	if (setjmp(jerr.setjmp_buffer)) {
-		/*
-		 * If we get here, the JPEG code has signaled an error.
-		 * We need to clean up the JPEG object, close the input file, and return.
-		 */
-		jpeg_destroy_decompress(&cinfo);
-		fclose(file);
-		return NULL;
-	}
+	jpeg_create_decompress(cinfo);
+	jpeg_stdio_src(cinfo, file);
+	jpeg_read_header(cinfo, TRUE);
 
-	jpeg_create_decompress(&cinfo);
-	jpeg_stdio_src(&cinfo, file);
-	jpeg_read_header(&cinfo, TRUE);
-	if (cinfo.image_width < 1 || cinfo.image_height < 1) {
+	if (cinfo->image_width < 1 || cinfo->image_height < 1) {
 		buffer[0] = NULL;	/* Initialize pointer to avoid spurious free in cleanup code */
 		RErrorCode = RERR_BADIMAGEFILE;
 		goto abort_and_release_resources;
 	}
 
-	buffer[0] = (JSAMPROW) malloc(cinfo.image_width * cinfo.num_components);
+	buffer[0] = (JSAMPROW) malloc(cinfo->image_width * cinfo->num_components);
 	if (!buffer[0]) {
 		RErrorCode = RERR_NOMEMORY;
 		goto abort_and_release_resources;
 	}
 
-	if (cinfo.jpeg_color_space == JCS_GRAYSCALE)
-		cinfo.out_color_space = JCS_GRAYSCALE;
+	if (cinfo->jpeg_color_space == JCS_GRAYSCALE)
+		cinfo->out_color_space = JCS_GRAYSCALE;
 	else
-		cinfo.out_color_space = JCS_RGB;
+		cinfo->out_color_space = JCS_RGB;
 
-	cinfo.quantize_colors = FALSE;
-	cinfo.do_fancy_upsampling = FALSE;
-	cinfo.do_block_smoothing = FALSE;
-	jpeg_calc_output_dimensions(&cinfo);
-	image = RCreateImage(cinfo.image_width, cinfo.image_height, False);
+	cinfo->quantize_colors = FALSE;
+	cinfo->do_fancy_upsampling = FALSE;
+	cinfo->do_block_smoothing = FALSE;
+	jpeg_calc_output_dimensions(cinfo);
+	image = RCreateImage(cinfo->image_width, cinfo->image_height, False);
 	if (!image) {
 		RErrorCode = RERR_NOMEMORY;
 		goto abort_and_release_resources;
 	}
 
-	jpeg_start_decompress(&cinfo);
+	jpeg_start_decompress(cinfo);
 	ptr = image->data;
-	if (cinfo.out_color_space == JCS_RGB) {
-		while (cinfo.output_scanline < cinfo.output_height) {
-			jpeg_read_scanlines(&cinfo, buffer, (JDIMENSION) 1);
+	if (cinfo->out_color_space == JCS_RGB) {
+		while (cinfo->output_scanline < cinfo->output_height) {
+			jpeg_read_scanlines(cinfo, buffer, (JDIMENSION) 1);
 			bptr = buffer[0];
-			memcpy(ptr, bptr, cinfo.image_width * 3);
-			ptr += cinfo.image_width * 3;
+			memcpy(ptr, bptr, cinfo->image_width * 3);
+			ptr += cinfo->image_width * 3;
 		}
 	} else {
-		while (cinfo.output_scanline < cinfo.output_height) {
-			jpeg_read_scanlines(&cinfo, buffer, (JDIMENSION) 1);
+		while (cinfo->output_scanline < cinfo->output_height) {
+			jpeg_read_scanlines(cinfo, buffer, (JDIMENSION) 1);
 			bptr = buffer[0];
-			for (i = 0; i < cinfo.image_width; i++) {
+			for (i = 0; i < cinfo->image_width; i++) {
 				*ptr++ = *bptr;
 				*ptr++ = *bptr;
 				*ptr++ = *bptr++;
 			}
 		}
 	}
 
-	jpeg_finish_decompress(&cinfo);
+	jpeg_finish_decompress(cinfo);
 
  abort_and_release_resources:
-	jpeg_destroy_decompress(&cinfo);
+	jpeg_destroy_decompress(cinfo);
 	fclose(file);
 	if (buffer[0])
 		free(buffer[0]);
 
 	return image;
 }
+
+RImage *RLoadJPEG(const char *file_name)
+{
+	struct jpeg_decompress_struct cinfo;
+	/* We use our private extension JPEG error handler.
+	 * Note that this struct must live as long as the main
+	 * JPEG parameter struct, to avoid dangling-pointer problems.
+	 */
+	struct my_error_mgr jerr;
+
+	cinfo.err = jpeg_std_error(&jerr.pub);
+	jerr.pub.error_exit = my_error_exit;
+	/* Establish the setjmp return context for my_error_exit to use. */
+	if (setjmp(jerr.setjmp_buffer)) {
+		/*
+		 * If we get here, the JPEG code has signaled an error.
+		 * We need to clean up the JPEG object, close the input file, and return.
+		 */
+		jpeg_destroy_decompress(&cinfo);
+		return NULL;
+	}
+	return do_read_jpeg_file(&cinfo, file_name);
+}