pcm_buffer: pcm_buffer_get() never returns NULL

This fixes a bug when libsamplerate returns an empty buffer for a very
small input buffer.  The caller thinks this is an error, bug there is
no GError object.

NEWS

@@ -1,4 +1,5 @@
 ver 0.16.8 (2012/??/??)
+* fix for libsamplerate assertion failure
 
 
 ver 0.16.7 (2012/02/04)

src/pcm_buffer.c

@@ -34,6 +34,11 @@ pcm_buffer_get(struct pcm_buffer *buffer, size_t size)
 {
 	assert(buffer != NULL);
 
+	if (size == 0)
+		/* never return NULL, because NULL would be assumed to
+		   be an error condition */
+		size = 1;
+
 	if (buffer->size < size) {
 		/* free the old buffer */
 		g_free(buffer->buffer);

src/pcm_buffer.h

@@ -63,6 +63,10 @@ pcm_buffer_deinit(struct pcm_buffer *buffer)
 /**
  * Get the buffer, and guarantee a minimum size.  This buffer becomes
  * invalid with the next pcm_buffer_get() call.
+ *
+ * This function will never return NULL, even if size is zero, because
+ * the PCM library uses the NULL return value to signal "error".  An
+ * empty destination buffer is not always an error.
  */
 G_GNUC_MALLOC
 void *