render/vulkan: Avoid double-free on calloc error

In query_modifier_support, the calloc for either or both of render_mods
and texture_mods may fail, in which case both are freed for convenience.
However, if one is non-NULL, vulkan_format_props_finish will try to free
it again.

NULL them to avoid double-free.

render/vulkan/pixel_format.c

@@ -401,6 +401,8 @@ static bool query_modifier_support(struct wlr_vk_device *dev,
 		free(modp.pDrmFormatModifierProperties);
 		free(props->dmabuf.render_mods);
 		free(props->dmabuf.texture_mods);
+		props->dmabuf.render_mods = NULL;
+		props->dmabuf.texture_mods = NULL;
 		return false;
 	}