Make sure parse_all stops on Errors (#472)

All uses of `Parser::parse_all` in the code immediately propagate errors
and thus stop iteration. However the Iterator interface does not mandate
this, and not handling the inner `Result` at all can way too easily lead
to infinite loops.

crates/wasmparser/src/parser.rs

@@ -700,7 +700,10 @@ impl Parser {
             }
             let payload = match cur.parse(data, true) {
                 // Propagate all errors
-                Err(e) => return Some(Err(e)),
+                Err(e) => {
+                    done = true;
+                    return Some(Err(e));
+                }
 
                 // This isn't possible because `eof` is always true.
                 Ok(Chunk::NeedMoreData(_)) => unreachable!(),
@@ -997,6 +1000,14 @@ mod tests {
         );
     }
 
+    #[test]
+    fn header_iter() {
+        for _ in Parser::default().parse_all(&[]) {}
+        for _ in Parser::default().parse_all(b"\0") {}
+        for _ in Parser::default().parse_all(b"\0asm") {}
+        for _ in Parser::default().parse_all(b"\0asm\x01\x01\x01\x01") {}
+    }
+
     fn parser_after_header() -> Parser {
         let mut p = Parser::default();
         assert_matches!(