Updates WebAddress to ignore the colon after the host component of a URL if no port is specified

Currently, the regex used to extract the port matches ':' followed by 1 or more
digits. This means that when passed a malformed URL of type <host>:<path>, no
match is made for the port and the ':' is matched as part of the path. Since the
handling of the path adds a leading '/' where absent (see http://b/1011602),
this leads to the URL being converted to <host>/:<path>.

This change updates the port regex to match ':' followed by zero or more digits.
This means that the ':' is always matched, so it does not leak into the path
and the result is <host><path>. This matches the behavior of desktop browsers.

Bug: 2494876
Change-Id: I34b47c8187cf03aa7674c14cd6593de53dce3169