radv: fix vertex buffer null descriptors

Fixes: 0f1ead7b536 "radv: handle NULL vertex bindings"
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6773>
diff --git a/src/amd/vulkan/radv_cmd_buffer.c b/src/amd/vulkan/radv_cmd_buffer.c
index f1b077e..6b3ccb7 100644
--- a/src/amd/vulkan/radv_cmd_buffer.c
+++ b/src/amd/vulkan/radv_cmd_buffer.c
@@ -2753,8 +2753,10 @@
 			unsigned num_records;
 			unsigned stride;
 
-			if (!buffer)
+			if (!buffer) {
+				memset(desc, 0, 4 * 4);
 				continue;
+			}
 
 			va = radv_buffer_get_va(buffer->bo);