Directory "foo:bar@1:23" destroys Emacs session on M-x tramp-unload-tramp

[rndusr]

Reproducing this issue is very simple:

1. Run `emacs -Q foo:bar@1:23/asdf` (the directory name is the relevant part)

2. M-x tramp-unload-tramp

Effects:

a) Error in minibuffer: ‘tramp-file-name-structure’ didn’t match!

b) Basic actions like entering text or C-x C-s do not work anymore and produce
   the error message:
   Recursive load: "/usr/share/emacs/26.1/lisp/net/tramp.elc",
   "/usr/share/emacs/26.1/lisp/net/tramp.elc", [...]

c) C-x C-c doesn't fully terminate Emacs. The Emacs process cannot be terminated
   by SIGTERM either, only by SIGKILL.

I'm not a tramp user but this issue still affects me: When I run Ivy's
insert-file after step 1 (see above) I'm having the same problems as described
above.

I'm running Emacs 26.1.