fix delete group signal issue when capture data is NULL

DSView/pv/sigsession.cpp

@@ -652,10 +652,13 @@ void SigSession::del_group()
                 j++;
             }
 
+            std::deque< boost::shared_ptr<data::GroupSnapshot> > &snapshots = _group_data->get_snapshots();
+            if (!snapshots.empty()) {
                 _group_data->get_snapshots().at((*i)->get_sec_index()).reset();
-            std::deque< boost::shared_ptr<data::GroupSnapshot> >::iterator k = _group_data->get_snapshots().begin();
+                std::deque< boost::shared_ptr<data::GroupSnapshot> >::iterator k = snapshots.begin();
                 k += (*i)->get_sec_index();
                 _group_data->get_snapshots().erase(k);
+            }
 
             (*i).reset();
             i = _group_traces.erase(i);

libsigrok4DSL/hardware/DSL/dscope.c

@@ -1916,7 +1916,7 @@ static void receive_transfer(struct libusb_transfer *transfer)
             struct sr_dev_inst *sdi = devc->cb_data;
             for (l = sdi->channels; l; l = l->next) {
                 struct sr_channel *probe = (struct sr_channel *)l->data;
-                channel_cnt ++;
+                channel_cnt++;
                 channel_en_cnt += probe->enabled;
             }
             if (channel_en_cnt == 0)