matroskadec: fix display_width/height = 0 handling

Fixes Ticket2424
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/matroskadec.c

@@ -321,8 +321,8 @@ static EbmlSyntax matroska_info[] = {
 
 static EbmlSyntax matroska_track_video[] = {
     { MATROSKA_ID_VIDEOFRAMERATE,     EBML_FLOAT,0, offsetof(MatroskaTrackVideo,frame_rate) },
-    { MATROSKA_ID_VIDEODISPLAYWIDTH,  EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_width) },
-    { MATROSKA_ID_VIDEODISPLAYHEIGHT, EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_height) },
+    { MATROSKA_ID_VIDEODISPLAYWIDTH,  EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_width), {.u=-1} },
+    { MATROSKA_ID_VIDEODISPLAYHEIGHT, EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_height), {.u=-1} },
     { MATROSKA_ID_VIDEOPIXELWIDTH,    EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_width) },
     { MATROSKA_ID_VIDEOPIXELHEIGHT,   EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_height) },
     { MATROSKA_ID_VIDEOCOLORSPACE,    EBML_BIN,  0, offsetof(MatroskaTrackVideo,color_space) },
@@ -1576,9 +1576,9 @@ static int matroska_read_header(AVFormatContext *s)
         if (track->type == MATROSKA_TRACK_TYPE_VIDEO) {
             if (!track->default_duration && track->video.frame_rate > 0)
                 track->default_duration = 1000000000/track->video.frame_rate;
-            if (!track->video.display_width)
+            if (track->video.display_width == -1)
                 track->video.display_width = track->video.pixel_width;
-            if (!track->video.display_height)
+            if (track->video.display_height == -1)
                 track->video.display_height = track->video.pixel_height;
             if (track->video.color_space.size == 4)
                 fourcc = AV_RL32(track->video.color_space.data);