rebase: collapse two nested if-conditions

Also change the order since it feel to me like it's more about
--collapse than it is about --keep.

Differential Revision: https://phab.mercurial-scm.org/D2711

hgext/rebase.py

@@ -605,9 +605,8 b' class rebaseruntime(object):'
             hg.updaterepo(repo, newwd, False)
 
         collapsedas = None
-        if not self.keepf:
-            if self.collapsef:
-                collapsedas = newnode
+        if self.collapsef and not self.keepf:
+            collapsedas = newnode
         clearrebased(ui, repo, self.destmap, self.state, self.skipped,
                      collapsedas, self.keepf, fm=fm)