Don't require calling DoNativeBeforeUpdate() with locked CS

Acquire the lock in wxProgressDialog::DoNativeBeforeUpdate() itself
instead of relying on the caller to do it.

This is just a refactoring in preparation for further changes.

include/wx/msw/progdlg.h

@@ -54,8 +54,9 @@ public:
     virtual WXWidget GetHandle() const wxOVERRIDE;
 
 private:
-    // Performs common routines to Update() and Pulse(). Requires the
+    // Common part of Update() and Pulse().
-    // shared object to have been entered.
+    //
+    // Returns false if the user requested cancelling the dialog.
     bool DoNativeBeforeUpdate(bool *skip);
 
     // Updates the various timing informations for both determinate

src/msw/progdlg.cpp

@@ -404,17 +404,19 @@ bool wxProgressDialog::Update(int value, const wxString& newmsg, bool *skip)
 #ifdef wxHAS_MSW_TASKDIALOG
     if ( HasNativeTaskDialog() )
     {
+        if ( !DoNativeBeforeUpdate(skip) )
+        {
+            // Dialog was cancelled.
+            return false;
+        }
+
+        value /= m_factor;
+
+        wxASSERT_MSG( value <= m_maximum, wxT("invalid progress value") );
+
         {
             wxCriticalSectionLocker locker(m_sharedData->m_cs);
 
-            // Do nothing in canceled state.
-            if ( !DoNativeBeforeUpdate(skip) )
-                return false;
-
-            value /= m_factor;
-
-            wxASSERT_MSG( value <= m_maximum, wxT("invalid progress value") );
-
             m_sharedData->m_value = value;
             m_sharedData->m_notifications |= wxSPDD_VALUE_CHANGED;
 
@@ -474,11 +476,13 @@ bool wxProgressDialog::Pulse(const wxString& newmsg, bool *skip)
 #ifdef wxHAS_MSW_TASKDIALOG
     if ( HasNativeTaskDialog() )
     {
-        wxCriticalSectionLocker locker(m_sharedData->m_cs);
-
-        // Do nothing in canceled state.
         if ( !DoNativeBeforeUpdate(skip) )
+        {
+            // Dialog was cancelled.
             return false;
+        }
+
+        wxCriticalSectionLocker locker(m_sharedData->m_cs);
 
         if ( !m_sharedData->m_progressBarMarquee )
         {
@@ -509,6 +513,8 @@ bool wxProgressDialog::DoNativeBeforeUpdate(bool *skip)
 #ifdef wxHAS_MSW_TASKDIALOG
     if ( HasNativeTaskDialog() )
     {
+        wxCriticalSectionLocker locker(m_sharedData->m_cs);
+
         if ( m_sharedData->m_skipped  )
         {
             if ( skip && !*skip )