extmod/modbluetooth: Fix descriptor registration with empty tuple.

Incorrect use of "continue" when the tuple was length zero meant it
broke the rest of the argument handling.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

extmod/modbluetooth.c

@@ -529,12 +529,9 @@ STATIC int bluetooth_gatts_register_service(mp_obj_t uuid_in, mp_obj_t character
 
         // Optional third element, iterable of descriptors.
         if (characteristic_len >= 3) {
-            mp_obj_t descriptors_len_in = mp_obj_len(characteristic_items[2]);
-            num_descriptors[characteristic_index] = mp_obj_get_int(descriptors_len_in);
-
-            if (num_descriptors[characteristic_index] == 0) {
-                continue;
-            }
+            mp_int_t n = mp_obj_get_int(mp_obj_len(characteristic_items[2]));
+            if (n) {
+                num_descriptors[characteristic_index] = n;
 
                 // Grow the flattened uuids and flags arrays with this many more descriptors.
                 descriptor_uuids = m_renew(mp_obj_bluetooth_uuid_t *, descriptor_uuids, descriptor_index, descriptor_index + num_descriptors[characteristic_index]);
@@ -567,6 +564,7 @@ STATIC int bluetooth_gatts_register_service(mp_obj_t uuid_in, mp_obj_t character
                 // Reflect that we've grown the handles array.
                 *num_handles += num_descriptors[characteristic_index];
             }
+        }
 
         characteristic_uuids[characteristic_index] = MP_OBJ_TO_PTR(uuid_obj);
         characteristic_flags[characteristic_index] = mp_obj_get_int(characteristic_items[1]);