Bug fixing related to stringtests failures on x86

Bug fixing related to stringtests failures on x86

Fixed Crash issues related to Strcat in the following cases
* StrcatPartialShorterSourceLen
* StrcatPartialEqualSourceLen
* StrcatPartialLongerSourceLen
* StrcatPartialZeroSourceLen

The failures were due to buffer overflow during memset.

Change-Id: Ie588c7288377bea59366e8e1ebf9fed78f4fe5b1
Signed-off-by: Ravi Nanjundappa <nravi.n@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1213
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>