Fix places in main where a negative return value could impact execution

Fix places in main where a negative return value could impact execution

This patch addresses a number of modules in main that did not handle the
negative return value from function calls adequately, or were not sufficiently
clear that the conditions leading to improper handling of the return values
could not occur.  This includes:

* asterisk.c: A negative return value from the read function would be used
directly as an index into a buffer.  We now check for success of the read
function prior to using its result as an index.

* manager.c: Check for failures in mkstemp and lseek when handling the
temporary file created for processing data returned from a CLI command in
action_command.  Also check that the result of an lseek is sanitized prior
to using it as the size of a memory map to allocate.

* translate.c: Note in the appropriate locations where powerof cannot return
a negative value, due to proper checks placed on the inputs to that function.

(issue ASTERISK-19655)
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/1863/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@362359 65c4cc65-6c06-0410-ace0-fbb531ad65f3