Add a fix for Surface Pro users who auto hide their taskbar

This is for https://github.com/adobe/brackets/issues/7555

This update fixes a problem for Surface Pro users with auto-hide taskbars that @bchintx found while testing on a 1st Gen Surface Pro.  

This may need further development as the underlying cause isn't clear but, because I don't have a Surface Pro to test with and it isn't very likely that a Surface Pro user is going to run Windows 8.1 with more than one monitor, this solution should be sufficient.  

@bchintx confirmed this so he should reconfirm with an official installer build after this has been merged.

@redmunds can you do a quick code review and let me know what you think and merge it if you think it's good to go?

I'll let @bchintx know when he can test it again.