Add a better fix for the $addr update problem

In general, initialising last_update_time to next_update_time upon
startup doesn't make sense, as some update functions check for the
distance between the two being higher than a given epsilon to prevent
updating too often. This means that they won't trigger when
update_stuff() is being run for the first time.

src/conky.c

@@ -6705,7 +6705,8 @@ static void main_loop(void)
 	sigaddset(&newmask, SIGUSR1);
 #endif
 
-	next_update_time = last_update_time = get_time();
+	last_update_time = 0.0;
+	next_update_time = get_time();
 	info.looped = 0;
 	while (terminate == 0 && (total_run_times == 0 || info.looped < total_run_times)) {
 		info.looped++;