Fix: Do not shut down fserve engine if not started up

This avoids a endless loop in a spin lock that has not been inited
yet if fserve engine was not started up by the time it was sent to
go down. This happened if icecast couldn't read the config because
the file was corrupted or non-existent.
Closes: #2144

src/fserve.c

@@ -66,6 +66,8 @@
 
 #define BUFSIZE 4096
 
+static volatile int __inited = 0;
+
 static fserve_t *active_list = NULL;
 static fserve_t *pending_list = NULL;
 
@@ -104,12 +106,17 @@ void fserve_initialize(void)
     fserve_recheck_mime_types (config);
     config_release_config();
 
+    __inited = 1;
+
     stats_event (NULL, "file_connections", "0");
     ICECAST_LOG_INFO("file serving started");
 }
 
 void fserve_shutdown(void)
 {
+    if (!__inited)
+        return;
+
     thread_spin_lock (&pending_lock);
     run_fserv = 0;
     while (pending_list)