Improve insert-text signal handler to block pasting text into the control,
which may overflow the specified max length in one action, and not only
entering individual characters.
See #3158.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72778 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775