Bugfix for attempt to perform arithmetic on field 'wxMOD_RAW_CONTROL' (a nil value).

Fix for:
	Lua: Error while running chunk
	src/editor/editor.lua:664: attempt to perform arithmetic on field 'wxMOD_RAW_CONTROL' (a nil value)
	stack traceback:
		src/editor/editor.lua:664: in function <src/editor/editor.lua:649>
		[C]: in function 'MainLoop'
		src/main.lua:442: in main chunk
		[C]: ?

which happens with 0.361 using Linux. This behaviour could also be present using Windows though unverified.