Merge branch 'dh/encoding-trace-optim'

An expensive operation to prepare tracing was done in re-encoding
code path even when the tracing was not requested, which has been
corrected.

* dh/encoding-trace-optim:
  convert: return early when not tracing

convert.c

@@ -324,6 +324,9 @@ static void trace_encoding(const char *context, const char *path,
 	struct strbuf trace = STRBUF_INIT;
 	int i;
 
+	if (!trace_want(&coe))
+		return;
+
 	strbuf_addf(&trace, "%s (%s, considered %s):\n", context, path, encoding);
 	for (i = 0; i < len && buf; ++i) {
 		strbuf_addf(