app_voicemail/IMAP: IMAP access FATAL error: Out of memory

app_voicemail/IMAP: IMAP access FATAL error: Out of memory

Sometimes uw-imap function 'mail_fetchbody' returns huge len
which then pass to uw-imap function 'rfc822_base64'.
uw-imap tries to allocate huge memory and abort() on fail.

This patch check the len.
If the len more than max size (128 Mbytes) log error.
This patch also set variables len, newlen to avoid uninizialezed len.
This patch also check pointer returned by rfc822_base64.

ASTERISK-25899 #close

Change-Id: I4a0e7d655f11abef6a5224e2169df6d5c1f1caca