Lock m_critsect in POSIX wxThread::Create().

This is the documented behavior: all methods accessing m_internal should
lock it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73997 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/threadpsx.cpp

@@ -1191,6 +1191,8 @@ wxThread::wxThread(wxThreadKind kind)
 
 wxThreadError wxThread::Create(unsigned int WXUNUSED_STACKSIZE(stackSize))
 {
+    wxCriticalSectionLocker lock(m_critsect);
+
     if ( m_internal->GetState() != STATE_NEW )
     {
         // don't recreate thread