Added a flag to avoid Capture/Release asserts

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@8187 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/sashwin.h

@@ -188,6 +188,7 @@ private:
     wxColour    m_darkShadowColour;
     wxColour    m_hilightColour;
     wxColour    m_faceColour;
+    bool        m_mouseCaptured;
 
 DECLARE_EVENT_TABLE()
 };