Call wxThread::Create() from Run() automatically.

Call wxThread::Create() from Run() automatically.

In the common case, when Run() is called immediately after Create() and
default stack size is used, it's unnecessarily verbose.  Just create the
thread in Run() if it wasn't done explicitly yet.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73999 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775