wxTextFile: don't loose data with CRCRLF line endings.

Previously, when reading files with completely nonstandard - but
occurring in the wild thanks to broken Notepad - files with CRCRLF, all
content would be replaced with empty lines.

Fix the code to do what many editors do with such files: treat this as
data line followed by an empty one. This is not ideal, but it is better
than discarding data - and arguably, silently cleaning up the endings
wouldn't be great either (and would add extra complications for what is
an obscure and broken case).

See http://stackoverflow.com/questions/6998506/text-file-with-0d-0d-0a-line-breaks

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75387 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775