mac text renderer: make sure our picture is of the right height.

This will likely fix #2649

modules/misc/quartztext.c

@@ -850,7 +850,7 @@ static int RenderYUVA( filter_t *p_filter, subpicture_region_t *p_region, UniCha
     fmt.i_chroma = VLC_CODEC_YUVA;
     fmt.i_aspect = 0;
     fmt.i_width = fmt.i_visible_width = i_width;
-    fmt.i_height = fmt.i_visible_height = i_textblock_height + VERTICAL_MARGIN * 2;
+    fmt.i_height = fmt.i_visible_height = __MIN( i_height, i_textblock_height + VERTICAL_MARGIN * 2);
     fmt.i_x_offset = fmt.i_y_offset = 0;
 
     p_region->p_picture = picture_New( fmt.i_chroma, fmt.i_width, fmt.i_height, fmt.i_aspect );