commands: exit from the log loop at the right time

Previously, we'd run the iterator one more time than necessary,
potentially doing a lot of extra work in the process.

mercurial/commands.py

@@ -4215,10 +4215,10 b' def log(ui, repo, *pats, **opts):'
         displayer.show(ctx, copies=copies, matchfn=revmatchfn)
 
     for ctx in cmdutil.walkchangerevs(repo, matchfn, opts, prep):
+        if displayer.flush(ctx.rev()):
+            count += 1
         if count == limit:
             break
-        if displayer.flush(ctx.rev()):
-            count += 1
     displayer.close()
 
 @command('manifest',