lib.Uri: Fix path join for empty authority

__new_with_path() joins base and path with exactly one '/', assuming a
trailing '/' in base is a path separator. That assumption breaks for
URIs with empty authority, where scheme_plus_authority ends in '://'
(e.g. 'file:///tmp/x'): new_replace_path('/etc/hosts') drops the
leading slash of the path and produces 'file://etc/hosts', which
parses with hostname 'etc' and path '/hosts' instead of path
'/etc/hosts'.

Treat a base ending in '://' separately and keep a leading slash in
the path, adding one if it is missing.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/Uri.py

@@ -156,6 +156,12 @@ class Uri:
         ret.__password = None
         if not path:
             return ret
+        if ret.__string.endswith('://'):
+            # -- Empty authority: the trailing '/' is part of the '://'
+            # separator, so a leading slash in path must be kept to stay
+            # an absolute path
+            ret.__string += path if path.startswith('/') else '/' + path
+            return ret
         if ret.__string[-1] == '/':
             if path[0] == '/':
                 ret.__string += path[1:]