new set of fixes for problems due to huge files support: drop wxFileSize_t, use wxFileOffset only, make wxInvalidOffset an int (main part of the patch 1063498)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30427 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/gifdecod.cpp

@@ -621,7 +621,7 @@ bool wxGIFDecoder::CanRead()
     if ( !m_f->Read(buf, WXSIZEOF(buf)) )
         return false;
 
-    m_f->SeekI(-(off_t)WXSIZEOF(buf), wxFromCurrent);
+    m_f->SeekI(-(wxFileOffset)WXSIZEOF(buf), wxFromCurrent);
 
     return memcmp(buf, "GIF", WXSIZEOF(buf)) == 0;
 }