lavf: remove unneeded pb check

Fixes CID747727
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -428,7 +428,7 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
         return AVERROR(EINVAL);
     }
 
-    if (!*fmt && pb && pb->av_class && av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type) >= 0 && mime_type) {
+    if (!*fmt && pb->av_class && av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type) >= 0 && mime_type) {
         if (!av_strcasecmp(mime_type, "audio/aacp")) {
             *fmt = av_find_input_format("aac");
         }