NullPointerException occures when openning Properties without a given resource

an additionan null check is added for the result of getResource() call. The following usages of
the result has such checks, so now it's being checked before the first use.

see: https://issues.jboss.org/browse/JBIDE-18260

Signed-off-by: vrubezhny <vrubezhny@exadel.com>
Merge pull request #116 from vrubezhny/npeInTernModulesPropertyPage

NullPointerException occures when openning Properties without a given re...