apps/app_voicemail: Trigger MWI notification with MixMonitor m() option

apps/app_voicemail: Trigger MWI notification with MixMonitor m() option

The MixMonitor m() option allows a recording to be pushed to a specific
voicemail mailbox. If the message is delivered to the mailbox's INBOX, however,
no MWI notification is currently raised.

This patch corrects the issue by properly calling notify_new_state from the
msg_create_from_file function. This will cause MWI to be triggered if the
message was placed in the mailbox's INBOX.

ASTERISK-24709 #close
Reported by: Gareth Palmer
patches:
  app_voicemail-430919.patch uploaded by Gareth Palmer (License 5169)
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Merged revisions 430920 from http://svn.asterisk.org/svn/asterisk/branches/11

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@430921 65c4cc65-6c06-0410-ace0-fbb531ad65f3