BUG/MINOR: deferred calling the libev socket timer callback function

On Linux systems with a newer cURL library (say ubuntu 22 which uses cURL
v7.81.0), the program crashes in the mir_curl_timer_cb() function (when
calling function mir_curl_ev_timer_cb()).

It was solved so that the call of the respective function is done via the
timer (and not directly as before).

This should fix GitHub issue #31.

Version of the program changed to v1.2.16.

VERSION

@@ -1 +1 @@
-1.2.15
+1.2.16

src/.build-counter

@@ -1 +1 @@
-2495
+2510

src/curl.c

@@ -444,13 +444,21 @@ static int mir_curl_timer_cb(CURLM *multi __maybe_unused, long timeout_ms, void
 
 	ev_timer_stop(curl->ev_base, &(curl->ev_timer));
 
-	if (timeout_ms > 0) {
+	/***
+	 * If the value of argument timeout_ms is less than 0, then the timer
+	 * should only be stopped; otherwise a timeout is set.
+	 */
+	if (timeout_ms >= 0) {
+		/***
+		 * If timeout is set to 0, we will delay calling the callback
+		 * function mir_curl_ev_timer_cb() by 1 millisecond.
+		 */
+		if (timeout_ms == 0)
+			timeout_ms = 1;
+
 		ev_timer_init(&(curl->ev_timer), mir_curl_ev_timer_cb, timeout_ms / 1000.0, 0.0);
 		ev_timer_start(curl->ev_base, &(curl->ev_timer));
 	}
-	else if (timeout_ms == 0) {
-		(void)mir_curl_ev_timer_cb(curl->ev_base, &(curl->ev_timer), 0);
-	}
 
 	ev_async_send(curl->ev_base, curl->ev_async);