Check for empty parameters before trying to restore a DB

First, the `$FULL` paramter wasn't checked on emptiness but it
can be empty if there is no backups present.
Second, `$FULL_INCR` may be empty too, so it has to be surrounded
by double quotes when tested in condition statements.

Change-Id: I4cc9522e800c996c29a1966e629759f7c5f8c8d3
Related-Bug: PROD-22068
1 file changed