added assertion capture of non-key frame

src/capture/capture_base.cpp

@@ -224,6 +224,8 @@ void CaptureBase::setProblem(ProblemPtr _problem)
     if (_problem == nullptr || _problem == this->getProblem())
         return;
 
+    assert(getFrame() and getFrame()->isKey());
+
     NodeBase::setProblem(_problem);
     registerNewStateBlocks(_problem);