pthreads: increase MAX_BUFFERS due to 24c043c9

This might fix a hypothetical memleak
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pthread.c

@@ -85,7 +85,7 @@ typedef struct ThreadContext {
 } ThreadContext;
 
 /// Max number of frame buffers that can be allocated when using frame threads.
-#define MAX_BUFFERS (32+1)
+#define MAX_BUFFERS (34+1)
 
 /**
  * Context used by codec threads and stored in their AVCodecContext thread_opaque.