ncm-altlogrotate: check the value of $overallglobal

If there is an entry named 'global', the @Globals list will be empty when reaching the if of line 138,
and if we don't check the value of $overallglobal (that is switched to 1 in case of an entry named 'global'),
then the block of code modifying the global configuration file will be skipped.

Author: StephaneGerardVUB