Clip editor: Sort tracks alphabetically when they have matched error

Is nice to ensure order of tracks when their error is the same or
is not known yet (the clip was not solved yet).

source/blender/blenkernel/intern/tracking.c

@@ -2904,6 +2904,10 @@ static int channels_average_error_sort(const void *a, const void *b)
     return 1;
   }
 
+  if (channel_a->track->error == channel_b->track->error) {
+    return channels_alpha_sort(a, b);
+  }
+
   return 0;
 }