fix(selector): cell range selector was not working when at bottom (#331)
fix(selector): cell range selector was not working when at bottom (#331)

* fix(selector): cell range selector was not working when at bottom
- the issue was that if user open the example "example-frozen-columns-and-rows-spreadsheet.html" and he scrolls completely at the bottom of the frozen grid (bottom right) and try to select a cell range, it was not selecting properly

* fix(selector): cell range selector work with frozen and regular grid

* refactor(selector): simplify the code and fix indentation and format

* refactor(selector): remove else condition but keep regular if

* refactor(selector): change code as per comment in PR

6pac/SlickGrid,6pac/SlickGrid