phabricator: fix processing of tags/desc in getoldnodedrevmap()

It seems that the previous logic was wrong (it essentially comes
from changeset 3ab0d5767b54 where the result got accumulated instead of
early returned).
First of all, the "continue" in first "if m:" is useless because we're
at the end of the loop. Then, the algorithm seems weird because we will
process all predecessors of a node and possibly override
`toconfirm[node]` for each of these having a tag (maybe this doesn't
happen, but still). Finally, we would also override `toconfirm[node]`
when the "Differential Revision: " is found in changeset description.
Maybe this is not a big deal when there is no mix of local tag and
changeset description update?

The logic is changed so that the loop on predecessors stops upon first
match of a tag and so that the changeset description is only checked if
no tag was found. Therefore, `toconfirm[node]` is only set once.

Differential Revision: https://phab.mercurial-scm.org/D7513

hgext/phabricator.py

@@ -403,12 +403,15 b' def getoldnodedrevmap(repo, nodelist):'
                     m = _differentialrevisiontagre.match(tag)
                     if m:
                         toconfirm[node] = (0, set(precnodes), int(m.group(1)))
-                        continue
-
-        # Check commit message
-        m = _differentialrevisiondescre.search(ctx.description())
-        if m:
-            toconfirm[node] = (1, set(precnodes), int(m.group('id')))
+                        break
+                else:
+                    continue  # move to next predecessor
+                break  # found a tag, stop
+        else:
+            # Check commit message
+            m = _differentialrevisiondescre.search(ctx.description())
+            if m:
+                toconfirm[node] = (1, set(precnodes), int(m.group('id')))
 
     # Double check if tags are genuine by collecting all old nodes from
     # Phabricator, and expect precursors overlap with it.