Fix possible buffer overflows & array out of bound

Fix possible buffer overflows & array out of bound

Init char buffer to null so we don't have to keep adding null
characters.
Fixed potential array out of bounds issue in
occollection::HandleBatchInterface()

Change-Id: Ief43e5196fe360e0035f8aff49b15d969fb92b5e
Signed-off-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/568
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Doug Hudson <douglas.hudson@intel.com>
Reviewed-by: Erich Keane <erich.keane@intel.com>