resource: resource path must have extension

src/resource/resource_id.cpp

@@ -13,6 +13,7 @@ namespace crown
 {
 ResourceId resource_id(const char* path)
 {
+	CE_ASSERT(path::extension(path) != NULL);
 	const char* type = path::extension(path);
 	const u32 len = u32(type - path - 1);
 	return resource_id(type, strlen32(type), path, len);