[BUGFIX] Call extension installer only with extension packages

Calling the TYPO3 extension installer with a root package
of a different type will lead to an exception to be thrown.

Move the install path check after the type check, to be sure
to call the installer only with extension types.

Resolves: #96028
Related: #96021
Releases: master, 11.5
Change-Id: Icdebc1a541a0b43461559e8f7a4a999fb1b327f3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72229


Tested-by: Simon Gilli <typo3@gilbertsoft.org>
Tested-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Simon Gilli <typo3@gilbertsoft.org>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>