Update SchedulerJobBeanImpl.java

For methods `getShortName` and `getShortGroup`, the implementation assumes the respective variables contain a period (`.`) which is true of jobs scheduled using the xml markup `<scheduler-entry>` methodology. However, if a user is programmatically scheduling jobs with custom `jobName` and/or `groupName` values, there is potential for IndexOutOfBounds exceptions due to `lastIndexOf` returning a -1.