Fix another bug in xwin.c causing a tmpfile in plbuf.c not to be closed.
Fix another bug in xwin.c causing a tmpfile in plbuf.c not to be closed.

svn path=/trunk/; revision=5250

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot