core: fix crash on plugin reload when using musl libs (closes #2052)

src/plugins/fifo/fifo-config.c

@@ -157,4 +157,5 @@ void
 fifo_config_free ()
 {
     weechat_config_free (fifo_config_file);
+    fifo_config_file = NULL;
 }

src/plugins/fifo/fifo.c

@@ -367,6 +367,9 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     weechat_plugin = plugin;
 
+    fifo_quiet = 0;
+    fifo_fd = -1;
+
     if (!fifo_config_init ())
         return WEECHAT_RC_ERROR;