#640 - Allows dots in package repo VSM path.
#640 - Handle case of plugin not found.

When plugin is removed and server restarted, then the material names of
package materials are not known, since the name is decided based on the
plugin. During VSM rendering, it will try and find the name, the name
will be empty and causes issues, without this check.
Merge pull request #664 from arvindsv/fix_vsm_for_packages

#640 - Fix VSM for package repository materials