speedo,w32: Fix silent user mode installation

* build-aux/speedo/w32/inst.nsi (AddToPath): Move account
check here.
(PrintNonAdminWarning): Remove is_user_install variable.

The PrintNonAdminWarning is not called in silent mode so the
variable was never set.

• Signed-off-by: Andre Heinecke <aheinecke@intevation.de>