template.c: flush stdout before the `perror` call

src/template.c

@@ -147,6 +147,7 @@ main(void)
 	// 1. open file
 	FILE* output_file = fopen(OUTPUT_FILE, "wb");
 	if (output_file == NULL) {
+		fflush(stdout);
 		perror("fopen");
 		return 1;
 	}