Merge branch 'msw-thread-priority'

Fix wxThread::SetPriority() documentation and avoid a spurious error
message.

Closes https://github.com/wxWidgets/wxWidgets/pull/1683

include/wx/thread.h

@@ -559,9 +559,6 @@ public:
     // priority
         // Sets the priority to "prio" which must be in 0..100 range (see
         // also wxPRIORITY_XXX constants).
-        //
-        // NB: under MSW the priority can only be set after the thread is
-        //     created (but possibly before it is launched)
     void SetPriority(unsigned int prio);
 
         // Get the current priority.

interface/wx/thread.h

@@ -1267,11 +1267,6 @@ public:
           - @c wxPRIORITY_DEFAULT: 50
           - @c wxPRIORITY_MAX: 100
 
-        Notice that in the MSW implementation the thread priority can currently
-        be only set after creating the thread with CreateThread(). But under
-        all platforms this method can be called either before launching the
-        thread using Run() or after doing it.
-
         Please note that currently this function is not implemented when using
         the default (@c SCHED_OTHER) scheduling policy under POSIX systems.
     */

src/msw/thread.cpp

@@ -606,6 +606,14 @@ void wxThreadInternal::SetPriority(unsigned int priority)
 {
     m_priority = priority;
 
+    if ( !m_hThread )
+    {
+        // The thread hasn't been created yet, so calling SetThreadPriority()
+        // right now would just result in an error -- just skip doing this, as
+        // the priority will be set when Create() is called later.
+        return;
+    }
+
     // translate wxWidgets priority to the Windows one
     int win_priority;
     if (m_priority <= 20)