Fix the incompatibility of gif saving

When cv2.imwirte() saves ".gif", it will cause _error: (-2:Unspecified error) could not find a writer for the specified extension in function 'cv::imwrite_'_. We add an if statement to check whether the saving file format is ".gif" so as to avoid the error.

tools/infer/predict_system.py

@@ -176,6 +176,8 @@ def main(args):
             draw_img_save = "./inference_results/"
             if not os.path.exists(draw_img_save):
                 os.makedirs(draw_img_save)
+            if flag:
+               image_file = image_file[:-3] + "png" 
             cv2.imwrite(
                 os.path.join(draw_img_save, os.path.basename(image_file)),
                 draw_img[:, :, ::-1])