patman: make "No recipient" checking more tolerant

If Series-to tag is missing, Patman exits with a message
"No recipient".

This is just annoying for those who had already added
sendemail.to configuration.

I guess many developers have

  [sendemail]
          to = u-boot@lists.denx.de

in their .git/config because the 'To: u-boot@lists.denx.de' field
should always be added when sending patches.

That seems more reasonable rather than adding
'Series-to: u-boot@lists.denx.de' to every patch series.

Patman should exit only when both Series-to tag and sendemail.to
configuration are mising.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>

tools/patman/gitutil.py

@@ -377,9 +377,14 @@ def EmailPatches(series, cover_fname, args, dry_run, raise_on_error, cc_fname,
     """
     to = BuildEmailList(series.get('to'), '--to', alias, raise_on_error)
     if not to:
-        print ("No recipient, please add something like this to a commit\n"
-            "Series-to: Fred Bloggs <f.blogs@napier.co.nz>")
-        return
+        git_config_to = command.Output('git', 'config', 'sendemail.to')
+        if not git_config_to:
+            print ("No recipient.\n"
+                   "Please add something like this to a commit\n"
+                   "Series-to: Fred Bloggs <f.blogs@napier.co.nz>\n"
+                   "Or do something like this\n"
+                   "git config sendemail.to u-boot@lists.denx.de")
+            return
     cc = BuildEmailList(series.get('cc'), '--cc', alias, raise_on_error)
     if self_only:
         to = BuildEmailList([os.getenv('USER')], '--to', alias, raise_on_error)