lavu/fifo: add av_fifo_alloc_array function

Allows to alloc fifo buffer by passing
number of elements and size of element.

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>

libavutil/fifo.h

@@ -41,6 +41,14 @@ typedef struct AVFifoBuffer {
  */
 AVFifoBuffer *av_fifo_alloc(unsigned int size);
 
+/**
+ * Initialize an AVFifoBuffer.
+ * @param nmemb number of elements
+ * @param size  size of the single element
+ * @return AVFifoBuffer or NULL in case of memory allocation failure
+ */
+AVFifoBuffer *av_fifo_alloc_array(size_t nmemb, size_t size);
+
 /**
  * Free an AVFifoBuffer.
  * @param f AVFifoBuffer to free