Add error handling if descriptionmsg isn't defined for extension.

Warning, Untested. Nobody likes fatals in the installer.
See bug 43817 comment 12.

Change-Id: I51453c38e59a635e8f0ad69e84daf2589750742f
Bug: 43817
Merge "Add error handling if descriptionmsg isn't defined for extension." into REL1_22