No changes, just use symbolic NO_IMAGE constant instead of -1 or wxNOT_FOUND.

No changes, just use symbolic NO_IMAGE constant instead of -1 or wxNOT_FOUND.

Existing declarations used -1 in several places to indicate the absence of the
image which wasn't especially clear and was also inconsistent with other
places that used wxNOT_FOUND which didn't make much sense in this context.

Add a new symbolic constant NO_IMAGE in wxWithImages and use it in the classes
deriving from it. This still doesn't help with wx{Tree,List}Ctrl but improves
clarity for the other classes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68810 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775