Use PBM_SETMARQUEE to implement indeterminate mode in wxMSW wxGauge.

The old code which simply used PBM_SETPOS after setting PBS_MARQUEE style
often worked but sometimes apparently didn't, so switch to the officially
sanctioned PBM_SETMARQUEE to implement this.

Also make wxGauge::SetDeterminateMode() and SetIndeterminateMode() methods
private as they are not part of the public class API.

Closes #11357.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64648 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/gauge.h

@@ -51,10 +51,7 @@ public:
     virtual bool SetForegroundColour(const wxColour& col);
     virtual bool SetBackgroundColour(const wxColour& col);
 
-
-    void SetIndeterminateMode();
-    void SetDeterminateMode();
-    void Pulse();
+    virtual void Pulse();
 
     WXDWORD MSWGetStyle(long style, WXDWORD *exstyle) const;
 
@@ -64,6 +61,15 @@ public:
 protected:
     virtual wxSize DoGetBestSize() const;
 
+private:
+    // returns true if the control is currently in indeterminate (a.k.a.
+    // "marquee") mode
+    bool IsInIndeterminateMode() const;
+
+    // switch to/from indeterminate mode
+    void SetIndeterminateMode();
+    void SetDeterminateMode();
+
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxGauge)
 };