[helper] corrected one of the convert frames ... function to work with numpy arrays

bob/pad/base/utils/helper_functions.py

@@ -87,13 +87,17 @@ def convert_list_of_frame_cont_to_array(frame_containers):
         An array containing features for all frames of all individuals.
     """
 
-    feature_vectors = []
 
+    if isinstance( frame_containers[0], bob.bio.video.FrameContainer): 
+
+      feature_vectors = []
       for frame_container in frame_containers:
           video_features_array = convert_frame_cont_to_array(
             frame_container)
 
       feature_vectors.append(video_features_array)
+    else: 
+      feature_vectors = frame_containers
 
     features_array = np.vstack(feature_vectors)