config: do not reset pos when braces found

When a brace is found, the config file should not seek back to before
the brace, otherwise the brace will be read multiple times.

sway/config.c

@@ -613,7 +613,9 @@ static int detect_brace(FILE *file) {
 		}
 	}
 	free(line);
-	fseek(file, pos, SEEK_SET);
+	if (ret == 0) {
+		fseek(file, pos, SEEK_SET);
+	}
 	return ret;
 }