esp8266/modnetwork: Protect scan() callback against memory errors.

scan() allocates memory so may cause an exception to be raised.

esp8266/modnetwork.c

@@ -136,6 +136,9 @@ STATIC void esp_scan_cb(scaninfo *si, STATUS status) {
         return;
     }
     if (si->pbss && status == 0) {
+        // we need to catch any memory errors
+        nlr_buf_t nlr;
+        if (nlr_push(&nlr) == 0) {
             struct bss_info *bs;
             STAILQ_FOREACH(bs, si->pbss, next) {
                 mp_obj_tuple_t *t = mp_obj_new_tuple(6, NULL);
@@ -147,6 +150,12 @@ STATIC void esp_scan_cb(scaninfo *si, STATUS status) {
                 t->items[5] = MP_OBJ_NEW_SMALL_INT(bs->is_hidden);
                 mp_obj_list_append(*esp_scan_list, MP_OBJ_FROM_PTR(t));
             }
+            nlr_pop();
+        } else {
+            mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+            // indicate error
+            *esp_scan_list = MP_OBJ_NULL;
+        }
     } else {
         // indicate error
         *esp_scan_list = MP_OBJ_NULL;