avformat/rtpdec_h264: Ignore framesize attributes without a height

Fixes: out of array read
Fixes: xfnEsbsbvEIX
Fixes: AISLE-2026-0111-00033
Stack out of array read Replicated through UnModified FFmpeg (ffprobe) with ASAN
Found-by: Joshua Rogers <joshua.rogers@aisle.com>

libavformat/rtpdec_h264.c

@@ -198,6 +198,9 @@ void ff_h264_parse_framesize(AVCodecParameters *par, const char *p)
         *dst++ = *p++;
     *dst = '\0';
 
+    if (*p != '-')
+        return;
+
     // a='framesize:96 320-240'
     // set our parameters
     par->width   = atoi(buf1);