Core git copes with URLs that have a colon after the port, but no actual
numeric value.  eg `http://example.com:/foo.git` or
`http://example.com:`.  That's horrible, but RFC 3986 says:

> URI producers and normalizers should omit the port component and its
> ":" delimiter if port is empty or if its value would be the same as
> that of the scheme's default.

Which indicates that they may and therefore we must accept it.

Test that we can handle URLs with a colon but no following port number.