Fix for file length fixup.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@63302 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/tarstrm.cpp

@@ -1299,6 +1299,11 @@ bool wxTarOutputStream::WriteHeaders(wxTarEntry& entry)
         m_tarsize += rounded;
 
         *m_extendedHdr = 0;
+
+        // update m_headpos which is used to seek back to fix up the file
+        // length if it is not known in advance
+        if (m_tarstart != wxInvalidOffset)
+            m_headpos = m_tarstart + m_tarsize;
     }
 
     // if don't have extended headers just report error