resolve_absolute_refuses_results_that_are_not_absolute resolved links against a
document at /home/u/docs/a.doc outside its cfg!(windows) branch. On Windows that
path is rooted but has no drive, so it is not absolute, resolve_absolute refuses
the result as documented, and the unwrap panicked. The Windows arm already covers
the same three cases with a drive. Found by the new docpath CI job on its first run.
resolve_absolute refuses a result that is not absolute on the running
platform, such as a relative link in a document that has no path yet.
It is the function to call before opening a file.