Fixed ConditionalAddTextStringToMap
Fixed ConditionalAddTextStringToMap

Refactoring changes the function to return an error in the 'null'
condition rather than remain a valid value.  This patch returns it to
its previous behavior by having it return 0

Change-Id: I7a3b42399dec2df3955f2b4ef513fa0ca7433bb8
Signed-off-by: Erich Keane <ec9f61fe526c14bb62c55d7c978f025ee6b3583d@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2212
Reviewed-by: Sakthivel Samidurai <2b42ef6ad9ddc9eb44e2c60668b448d90a7d2d41@intel.com>
Reviewed-by: Omkar Hegde <2f73167d782cd137889359cdea8329848f05c29a@intel.com>
Tested-by: jenkins-iotivity <09cb29e8a2b473a2c978382eec13ee06fa017bda@opendaylight.org>

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