fix: Failed to calculate the math Function on DSO mode

DSView/pv/dialogs/mathoptions.cpp

@@ -216,7 +216,10 @@ void MathOptions::accept()
                 dsoSig2 = dsoSig;
         }
     }
-    _session->math_rebuild(enable, dsoSig1, dsoSig2, type);
+
+    if (dsoSig1 != NULL && dsoSig2 != NULL){
+        _session->math_rebuild(enable, dsoSig1, dsoSig2, type);
+    }    
 }
 
 void MathOptions::reject()

DSView/pv/sigsession.cpp

@@ -1438,6 +1438,9 @@ namespace pv
     {
         ds_lock_guard lock(_data_mutex);
 
+        assert(dsoSig1);
+        assert(dsoSig2);
+
         auto math_stack = new data::MathStack(this, dsoSig1, dsoSig2, type);
         DESTROY_OBJECT(_math_trace);
         _math_trace = new view::MathTrace(enable, math_stack, dsoSig1, dsoSig2);

DSView/pv/view/trace.cpp

@@ -133,6 +133,10 @@ int Trace::get_type()
 
 int Trace::get_index()
 {
+    if(_index_list.size() == 0){
+        assert(false);
+    }
+    
     return _index_list.front();
 }
 
@@ -143,7 +147,9 @@ std::list<int> Trace::get_index_list()
 
 void Trace::set_index_list(const std::list<int> &index_list)
 {
-    assert(index_list.size() != 0);
+    if (index_list.size() == 0){
+        assert(false);
+    }
 
     _index_list = index_list;
 }