Warning fixes found under hardest mode of OpenWatcom. Seems clean in Borland, MinGW and DMC.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@29660 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/filedlgg.cpp

@@ -218,7 +218,7 @@ void wxFileData::ReadData()
         }
     }
 
-    m_size = buff.st_size;
+    m_size = (long)buff.st_size;
 
     m_dateTime = buff.st_mtime;