Bug Fix for #418 - Graph<T>::removeNode has potential to throw due to optional being accessed early

[Ajay-26]

Pull Request for Bug #418.

• Issue: Graph::removeNode does not check whether the node to be removed is actually present in the graph.
• Changes: Graph::removeNode now checks whether the std::optional node obtained from Graph::getNode() is indeed present in the Graph or not. If not present, the function does nothing. There is also a test called Test_removeInvalidNode within GraphTest.cpp.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.87%. Comparing base (1b31e63) to head (6f4e654). Report is 23 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #430 +/- ## ========================================== + Coverage 97.58% 97.87% +0.29% ========================================== Files 87 87 Lines 9492 10083 +591 Branches 0 666 +666 ========================================== + Hits 9263 9869 +606 + Misses 229 214 -15 ``` | [Flag](https://app.codecov.io/gh/ZigRazor/CXXGraph/pull/430/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ZigRazor) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/ZigRazor/CXXGraph/pull/430/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ZigRazor) | `97.87% <100.00%> (+0.29%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ZigRazor#carryforward-flags-in-the-pull-request-comment) to find out more.

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[ZigRazor]

It's ok, we can wait to merge this due to the license change? What do you think @sbaldu @nolankramer ?