ffmpeg: dont match unspecified media types in MATCH_PER_TYPE_OPT

This would change existing behavior, and should if done, done seperately.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg_opt.c

@@ -59,7 +59,7 @@
     int i, ret;\
     for (i = 0; i < o->nb_ ## name; i++) {\
         char *spec = o->name[i].specifier;\
-        if (!strcmp(spec, mediatype) || !*spec)\
+        if (!strcmp(spec, mediatype))\
             outvar = o->name[i].u.type;\
         else if (ret < 0)\
             exit_program(1);\