Add a av_fast_malloc function and replace several uses of av_fast_realloc,

thus avoiding potential memleaks and pointless memcpys.

Originally committed as revision 18470 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/utils.c

@@ -80,6 +80,17 @@ void *av_fast_realloc(void *ptr, unsigned int *size, unsigned int min_size)
     return ptr;
 }
 
+void av_fast_malloc(void *ptr, unsigned int *size, unsigned int min_size)
+{
+    void **p = ptr;
+    if (min_size < *size)
+        return;
+    *size= FFMAX(17*min_size/16 + 32, min_size);
+    av_free(*p);
+    *p = av_malloc(*size);
+    if (!*p) *size = 0;
+}
+
 /* encoder management */
 static AVCodec *first_avcodec = NULL;