Remove an unnecessary null pointer check
[An extra null pointer check is not needed](https://isocpp.org/wiki/faq/freestore-mgmt#delete-handles-null) in [the destructor for the class "TriMeshView"](https://github.com/zddhub/opensse/blob/e9223e6a2a89510e413af22453bfa97a1ee71bff/gui/SketchSearchDemo/trimeshview/trimeshview.cpp#L86).
