vp8enc, vp9enc: reset multipass file index when stopping encoder

Fixes multipass encoding when re-using the same element/pipeline
for subsequent encoding runs.

https://bugzilla.gnome.org/show_bug.cgi?id=747728

ext/vpx/gstvp8enc.c

@@ -1461,6 +1461,10 @@ gst_vp8_enc_stop (GstVideoEncoder * video_encoder)
 
   gst_tag_setter_reset_tags (GST_TAG_SETTER (encoder));
 
+  g_free (encoder->multipass_cache_file);
+  encoder->multipass_cache_file = NULL;
+  encoder->multipass_cache_idx = 0;
+
   return TRUE;
 }
 

ext/vpx/gstvp9enc.c

@@ -1434,6 +1434,10 @@ gst_vp9_enc_stop (GstVideoEncoder * video_encoder)
 
   gst_tag_setter_reset_tags (GST_TAG_SETTER (encoder));
 
+  g_free (encoder->multipass_cache_file);
+  encoder->multipass_cache_file = NULL;
+  encoder->multipass_cache_idx = 0;
+
   return TRUE;
 }