Hi,

On OSX when calling auth-source-search to search from keychain with
account has '\' in it, the function doesn't return user info back but
only password. This patch is to fix smtpmail if for whatever reason
above situation happened.

Long term is to fix auth-source-search. Looks like it missed this case
in auth-source-macos-keychain-search-items. If account has '\' in it,
security will return something like:

"acct"<blob>=0x414E545C6A756E68616F  "ANT\134junhao"

instead of form current code expects:

"acct"<blob>="junhao"

Even auth-source-search is fixed, I still think this patch is nice
to have to make smtpmail more robust.

Thanks - Jun