demux: minibox: fix dead loop

modules/codec/substx3g.c

@@ -369,7 +369,8 @@ static int Decode( decoder_t *p_dec, block_t *p_block )
     subpicture_updater_sys_t *p_spu_sys = p_spu->updater.p_sys;
 
     mp4_box_iterator_t it;
-    mp4_box_iterator_Init( &it, p_block->p_buffer, p_block->i_buffer );
+    mp4_box_iterator_Init( &it, p_buf,
+                           p_block->i_buffer - (p_buf - p_block->p_buffer) );
     /* Parse our styles */
     while( mp4_box_iterator_Next( &it ) )
     {

modules/demux/mp4/minibox.h

@@ -50,6 +50,7 @@ static bool mp4_box_iterator_Next( mp4_box_iterator_t *p_it )
             p_it->i_buffer -= i_size;
             return true;
         }
+        else break;
     }
     return false;
 }