[BUGFIX] Install Tool: Error message gives wrong info

Based on issue #45135 the change not only includes the
check for the variable length for typo_db_password, but
for typo_db, typo_db_host and typo_db_username as well.

Resolves: #45135
Releases: 4.5,4.7,6.0,6.1
Change-Id: Idf8998cb1d648e89d59ba9641222e608df332300
Reviewed-on: https://review.typo3.org/18326
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer