skip fast_gettext initialization if the locale directory does not exist

avoid "load failed:path /usr/share/YaST2/locale cound not be found!" error
in testsuite during yast2 package build in OBS

the directory is owned by yast2 package and it does not exist yet when
the package is being built
Merge pull request #61 from lslezak/fast_gettext_initialization_fix

skip fast_gettext initialization if the locale directory does not exist