fix potential memleak.

(cherry picked from commit e348132d)
Signed-off-by: Rémi Duraffort <ivoire@videolan.org>

modules/video_filter/erase.c

@@ -163,6 +163,7 @@ static int Create( vlc_object_t *p_this )
     if( !psz_filename )
     {
         msg_Err( p_filter, "Missing 'mask' option value." );
+        free( p_sys );
         return VLC_EGENERIC;
     }