phabricator: teach {phabreview} to work without --amend

There's some possibility of this being wrong (e.g. if the url config was
changed).  But commit messages can be amended too, so that isn't bulletproof
either.  Having something seems better than just returning None.

hgext/phabricator.py

@@ -997,3 +997,17 b' def template_review(context, mapping):'
             b'url': m.group(b'url'),
             b'id': b"D{}".format(m.group(b'id')),
         })
+    else:
+        tags = ctx.repo().nodetags(ctx.node())
+        for t in tags:
+            if _differentialrevisiontagre.match(t):
+                url = ctx.repo().ui.config(b'phabricator', b'url')
+                if not url.endswith(b'/'):
+                    url += b'/'
+                url += t
+
+                return templateutil.hybriddict({
+                    b'url': url,
+                    b'id': t,
+                })
+    return None

tests/test-phabricator.t

@@ -106,13 +106,13 b' behind to identify it.'
 Template keywords
   $ hg log -T'{rev} {phabreview|json}\n'
   3 {"id": "D5545", "url": "https://phab.mercurial-scm.org/D5545"}
-  2 null
+  2 {"id": "D5544", "url": "https://phab.mercurial-scm.org/D5544"}
   1 {"id": "D4597", "url": "https://phab.mercurial-scm.org/D4597"}
   0 {"id": "D4596", "url": "https://phab.mercurial-scm.org/D4596"}
 
   $ hg log -T'{rev} {if(phabreview, "{phabreview.url} {phabreview.id}")}\n'
   3 https://phab.mercurial-scm.org/D5545 D5545
-  2 
+  2 https://phab.mercurial-scm.org/D5544 D5544
   1 https://phab.mercurial-scm.org/D4597 D4597
   0 https://phab.mercurial-scm.org/D4596 D4596