filter, stream: Fix error check for DMA-BUF buffers

When a buffer is of type SPA_DATA_DmaBuf, the 'data' field
will be NULL - we instead have to check if the file descriptor
is valid. The current code, however, always checks if the
data is NULL, which gives a false positive for DMA-BUF buffers,
signaling an error when there is none.

Fix that by also checking if the buffer type is MemPtr together
with the NULL check of the 'data' field.

src/pipewire/filter.c

@@ -684,7 +684,7 @@ static int impl_port_use_buffers(void *object,
 						return res;
 					SPA_FLAG_SET(b->flags, BUFFER_FLAG_MAPPED);
 				}
-				else if (d->data == NULL) {
+				else if (d->type == SPA_DATA_MemPtr && d->data == NULL) {
 					pw_log_error(NAME" %p: invalid buffer mem", filter);
 					return -EINVAL;
 				}

src/pipewire/stream.c

@@ -687,7 +687,7 @@ static int impl_port_use_buffers(void *object,
 						return res;
 					SPA_FLAG_SET(b->flags, BUFFER_FLAG_MAPPED);
 				}
-				else if (d->data == NULL) {
+				else if (d->type == SPA_DATA_MemPtr && d->data == NULL) {
 					pw_log_error(NAME" %p: invalid buffer mem", stream);
 					return -EINVAL;
 				}