Fix CreateDecodedNAL return

modules/demux/mpeg/hevc.c

@@ -229,7 +229,7 @@ static uint8_t * CreateDecodedNAL( int *pi_ret,
 {
     uint8_t *dst = malloc( i_src );
     if( !dst )
-        return;
+        return NULL;
 
     *pi_ret = nal_decode( src, dst, i_src );
     return dst;