iridium: don't try to update signal quality if not registered

Seems that launching AT+CSQF when not registered ends up timing out. AT+CSQF
is meant to be the fast version to get the signal quality, and is expected to
return instantly with the last cached signal quality value. But if we never
got registered, there is no such cached value, so it probably waits to get the
first one.

plugins/mm-modem-iridium-gsm.c

@@ -383,6 +383,16 @@ get_signal_quality (MMModemGsmNetwork *modem,
 
     info = mm_callback_info_uint_new (MM_MODEM (modem), callback, user_data);
 
+    /* If modem is not registered, don't even bother trying to get signal
+     * quality */
+    if (mm_modem_get_state (MM_MODEM (modem)) < MM_MODEM_STATE_REGISTERED) {
+        mm_dbg ("Not getting signal quality, not registered yet");
+        mm_generic_gsm_update_signal_quality (MM_GENERIC_GSM (info->modem), 0);
+        mm_callback_info_set_result (info, GUINT_TO_POINTER (0), NULL);
+        mm_callback_info_schedule (info);
+        return;
+    }
+
     /* The iridium modem may have a huge delay to get signal quality if we pass
      * AT+CSQ, so we'll default to use AT+CSQF, which is a fast version that
      * returns right away the last signal quality value retrieved */