Fix the uniform set creation of multimesh with a invalidated buffer

servers/rendering/renderer_rd/storage_rd/mesh_storage.h

@@ -615,6 +615,9 @@ public:
 	_FORCE_INLINE_ RID multimesh_get_3d_uniform_set(RID p_multimesh, RID p_shader, uint32_t p_set) const {
 		MultiMesh *multimesh = multimesh_owner.get_or_null(p_multimesh);
 		if (!multimesh->uniform_set_3d.is_valid()) {
+			if (!multimesh->buffer.is_valid()) {
+				return RID();
+			}
 			Vector<RD::Uniform> uniforms;
 			RD::Uniform u;
 			u.uniform_type = RD::UNIFORM_TYPE_STORAGE_BUFFER;
@@ -630,6 +633,9 @@ public:
 	_FORCE_INLINE_ RID multimesh_get_2d_uniform_set(RID p_multimesh, RID p_shader, uint32_t p_set) const {
 		MultiMesh *multimesh = multimesh_owner.get_or_null(p_multimesh);
 		if (!multimesh->uniform_set_2d.is_valid()) {
+			if (!multimesh->buffer.is_valid()) {
+				return RID();
+			}
 			Vector<RD::Uniform> uniforms;
 			RD::Uniform u;
 			u.uniform_type = RD::UNIFORM_TYPE_STORAGE_BUFFER;