Button: prevent crashes caused by _isWithinBounds

[XeduR]

There's currently a chance that the button's touch event is still called after the button's view.parent has already been removed and set to nil. This will result in a runtime error within function widget._isWithinBounds( object, event ) when it attempts to index a nil value (i.e. object.contentBounds within object as it isn't a table anymore).

framework-widget/widgetLibrary/widget.lua

Lines 245 to 257 in d425ae7

	function widget._isWithinBounds( object, event )
	local bounds = object.contentBounds
	local x, y = event.x, event.y
	local isWithinBounds = true
	if "table" == type( bounds ) then
	if "number" == type( x ) and "number" == type( y ) then
	isWithinBounds = bounds.xMin <= x and bounds.xMax >= x and bounds.yMin <= y and bounds.yMax >= y
	end
	end
	return isWithinBounds
	end

The safest and easiest way to fix this issue is to just check that the button's view.parent exists and is still a display object at the start of the touch listener.

As a part of these changes, there's no need for further checks to see if the parent view exists given that the function won't get past the new initial check if it doesn't.

[XeduR]

Could you take a look at this PR @Shchvova?