Add condition for read_from_disc_checkbox in main_window

A condition has been added to check for the status of the 'read_from_disc_checkbox' in main_window.py. When checked, it clears the text from the 'source_folder_widget' and 'source_file_widget'. When unchecked, it continues with the existing check which ensures either source folder or source file is set but not both.

bd_to_avp/gui/main_window.py

@@ -338,9 +338,15 @@ def toggle_processing(self) -> None:
             self.processing_output_textedit.clear()
             source_folder_set = bool(self.source_folder_widget.text())
             source_file_set = bool(self.source_file_widget.text())
-            if (source_folder_set and source_file_set) or (not source_folder_set and not source_file_set):
-                QMessageBox.warning(self, "Warning", "Either Source Folder or Source File must be set, but not both.")
-                return
+            if self.read_from_disc_checkbox.isChecked():
+                self.source_folder_widget.set_text("")
+                self.source_file_widget.set_text("")
+            else:
+                if (source_folder_set and source_file_set) or (not source_folder_set and not source_file_set):
+                    QMessageBox.warning(
+                        self, "Warning", "Either Source Folder or Source File must be set, but not both."
+                    )
+                    return
 
             self.start_processing()