Fixed NULL-pointer dereferencing bug that was causing code death under Linux and SunOS.  Why does HPUX let me get away with this?  Sigh.
Fixed NULL-pointer dereferencing bug that was causing code death under
Linux and SunOS.  Why does HPUX let me get away with this?  Sigh.

svn path=/trunk/; revision=1728

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