* backport [18601] [18602]

Don't allow negative offsets when blending subpictures

src/video_output/vout_subpictures.c

@@ -728,6 +728,9 @@ void spu_RenderSubpictures( spu_t *p_spu, video_format_t *p_fmt,
 
             }
             
+            i_x_offset = __MAX( i_x_offset, 0 );
+            i_y_offset = __MAX( i_y_offset, 0 );
+
             if( p_spu->i_margin != 0 && p_spu->b_force_crop == VLC_FALSE )
             {
                 int i_diff = 0;
@@ -800,6 +803,9 @@ void spu_RenderSubpictures( spu_t *p_spu, video_format_t *p_fmt,
                 }
             }
 
+            i_x_offset = __MAX( i_x_offset, 0 );
+            i_y_offset = __MAX( i_y_offset, 0 );
+
             p_spu->p_blend->pf_video_blend( p_spu->p_blend, p_pic_dst,
                 p_pic_src, &p_region->picture, i_x_offset, i_y_offset,
                 i_fade_alpha * p_subpic->i_alpha / 255 );