ui-shared: do not allow negative minutes

Do to timestamp differences, sometimes cgit would should "-0 min", which
doesn't make any sense.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui-shared.c

@@ -596,6 +596,8 @@ void cgit_print_age(time_t t, time_t max_relative, const char *format)
 		return;
 	time(&now);
 	secs = now - t;
+	if (secs < 0)
+		secs = 0;
 
 	if (secs > max_relative && max_relative >= 0) {
 		cgit_print_date(t, format, ctx.cfg.local_time);