mxfdec: Fix CID 732262

Coverity thinks ofs can end up 15, thus writing past the end of layout[]. This
is incorrect since it's always incremented by 2. Checking ofs <= 14 makes
Coverity happy and doesn't hurt.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mxfdec.c

@@ -782,14 +782,14 @@ static int mxf_read_index_table_segment(void *arg, AVIOContext *pb, int tag, int
 static void mxf_read_pixel_layout(AVIOContext *pb, MXFDescriptor *descriptor)
 {
     int code, value, ofs = 0;
-    char layout[16] = {0};
+    char layout[16] = {0}; /* not for printing, may end up not terminated on purpose */
 
     do {
         code = avio_r8(pb);
         value = avio_r8(pb);
         av_dlog(NULL, "pixel layout: code %#x\n", code);
 
-        if (ofs < 16) {
+        if (ofs <= 14) {
             layout[ofs++] = code;
             layout[ofs++] = value;
         }