fix: only check for obsolete commits in the --rev case

With both `--all` and `--source`, we already exclude obsolete
revisions in the revset, so there's no need to call
`checkfixablectx()` in those cases.

Differential Revision: https://phab.mercurial-scm.org/D9227

hgext/fix.py

@@ -427,8 +427,8 b' def getrevstofix(ui, repo, opts):'
         revs = set(scmutil.revrange(repo, opts[b'rev']))
         if opts.get(b'working_dir'):
             revs.add(wdirrev)
-    for rev in revs:
-        checkfixablectx(ui, repo, repo[rev])
+        for rev in revs:
+            checkfixablectx(ui, repo, repo[rev])
     # Allow fixing only wdir() even if there's an unfinished operation
     if not (len(revs) == 1 and wdirrev in revs):
         cmdutil.checkunfinished(repo)