Fix format string in wxLog::LogLastRepeatIfNeeded().

Fix format string in wxLog::LogLastRepeatIfNeeded().

We used a format string without any format specifiers in it in a call to
wxString::Printf() which always had a parameter resulting in an assert failure
about a mismatch between the string and parameter count.

Fix this by using a separate Printf() call for this case.

Closes #13613.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69678 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775