Parsing an URL can never fail. The regexp is designed to match any
input. In the worst case, everything will end up in the "path"
component. WebPositive relies on this to generate file URLs from a plain
path.
URLs without a protocol are also possible, and can be used with an
implicit protocol. A typical example is network shares sometimes noted in
"//host.domain/path/file" form.
Add tests for these two cases and fix the parser to behave as expected.
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