Compilation fix after r75765.

Forgot to backport ResetAlpha() addition which is used by the code of r75765.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75772 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/bitmap.h

@@ -171,6 +171,7 @@ public:
     // disappear in the future
     bool HasAlpha() const;
     void UseAlpha();
+    void ResetAlpha();
 
     // support for scaled bitmaps
     virtual double GetScaleFactor() const { return 1.0; }

src/msw/bitmap.cpp

@@ -1241,6 +1241,12 @@ void wxBitmap::UseAlpha()
         GetBitmapData()->m_hasAlpha = true;
 }
 
+void wxBitmap::ResetAlpha()
+{
+    if ( GetBitmapData() )
+        GetBitmapData()->m_hasAlpha = false;
+}
+
 bool wxBitmap::HasAlpha() const
 {
     return GetBitmapData() && GetBitmapData()->m_hasAlpha;