Explicitly cast size_t to int to suppress MSVC warnings.

Implicit size_t-to-int conversions provoke warnings when building 64 bit
version (in which sizeof(size_t) > sizeof(int)) with MSVC, so make them
explicit as the size_t values used here will always fit in int range.

Closes #14113.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70940 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/grid.h

@@ -811,7 +811,7 @@ public:
 
     // these are pure virtual in wxGridTableBase
     //
-    virtual int GetNumberRows() { return m_data.size(); }
+    virtual int GetNumberRows() { return static_cast<int>(m_data.size()); }
     virtual int GetNumberCols() { return m_numCols; }
     virtual wxString GetValue( int row, int col );
     virtual void SetValue( int row, int col, const wxString& s );