Fix for #205

[mackenzieajudd]

It turned out that mouseMoveHandler was not correctly handling mouse positions of 0, treating it as falsy and falling back on other event properties. The fall-through case was also unhandled, resulting in an undefined exception.

Added new getMousePosition function to the controller so it could be individually unit tested and updated it to check for existence of mousePosition properties. If getMousePosition fails to find a valid position on the event it will return null and mouseMoveHandler will not requestAnimationFrame.

[cht8687]

Could anyone check this pull request and merge if you can? It fixed the issue with drag the splitter far left to the screen which caused the error 'Cannot read property '0' of undefined'...

[rjayagopal]

Hi @SomeKittens - Could you please help to merge this pull request? It fixes splitter far left drag issue leading to "Cannot read property0 of undefined". Appreciate your help.