Fix tracing when GIT_TRACE is set to an empty string.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

trace.c

@@ -55,7 +55,8 @@ static int get_trace_fd(int *need_close)
 {
 	char *trace = getenv("GIT_TRACE");
 
-	if (!trace || !strcmp(trace, "0") || !strcasecmp(trace, "false"))
+	if (!trace || !strcmp(trace, "") ||
+	    !strcmp(trace, "0") || !strcasecmp(trace, "false"))
 		return 0;
 	if (!strcmp(trace, "1") || !strcasecmp(trace, "true"))
 		return STDERR_FILENO;