handle: consolidate allowed url check

Do the check in handle instead of the two callers. This also
reduces the uses of handle::get_base_url
7 jobs for handle in 26 minutes and 40 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #181313
fedora test

00:07:14

 
  Lint
manual #181315
allowed to fail manual
clippy
passed #181314
rustfmt

00:00:26

passed #181316
tarball

00:10:32

 
  Cross Distro
passed #181319
debian_i386:testing

00:08:51

passed #181318
debian:testing

00:08:15

passed #181317
fedora:rawhide

00:08:10