If gmtime returns NULL since the input is negative (this happens for the MinGW compiler, but not for gcc on Linux), the operation is aborted. Example 29 doesn't crash anymore.
If gmtime returns NULL since the input is negative (this happens for the MinGW compiler, but not for gcc on Linux), the operation is aborted. Example 29 doesn't crash anymore.

svn path=/trunk/; revision=9014

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