Fixed issue if outside bounds of rows and cols.

[AdrianEPPlus]

Before submitting this pull request I have...

• [x] read EPPlus Softwares Contribution Guidlines
• [x] ensured that the functionality I have added/changed is covered by new unit tests.
• [x] merged the target branch into the PR branch and resolved any merge conflicts
• [x] Run all the unit tests and ensured that they all are green (unless the purpose of the PR is to provide us with failing unit tests).