Selecting non images leads to 400 error (cvat-ai#734)

* Fix HTTP 400 error if together with vision data the user submit non-vision data (e.g. text files)
* Ignore SVG images because Pillow doesn't work with them.

cvat/apps/engine/media_extractors.py

@@ -225,7 +225,9 @@ def _is_video(path):
 
 def _is_image(path):
     mime = mimetypes.guess_type(path)
-    return mime[0] is not None and mime[0].startswith('image')
+    # Exclude vector graphic images because Pillow cannot work with them
+    return mime[0] is not None and mime[0].startswith('image') and \
+        not mime[0].startswith('image/svg')
 
 def _is_dir(path):
     return os.path.isdir(path)

cvat/apps/engine/task.py

@@ -166,7 +166,12 @@ def _validate_data(data):
     def count_files(file_mapping, counter):
         for rel_path, full_path in file_mapping.items():
             mime = get_mime(full_path)
-            counter[mime].append(rel_path)
+            if mime in counter:
+                counter[mime].append(rel_path)
+            else:
+                slogger.glob.warn("Skip '{}' file (its mime type doesn't "
+                    "correspond to a video or an image file)".format(full_path))
+
 
     counter = { media_type: [] for media_type in MEDIA_TYPES.keys() }