Add null checking for observe request in easy setup

Checking if entityHandlerRequest is NULL is added.

Change-Id: I79bf75c9f53f28b9c0c679a5dd7371552764b5cd
Signed-off-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/13323Reviewed-by: Heewon Park <h_w.park@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>

service/easy-setup/enrollee/src/resourcehandler.c

@@ -1223,7 +1223,7 @@ OCEntityHandlerResult OCEntityHandlerCb(OCEntityHandlerFlag flag,
             ehRet = OC_EH_ERROR;
         }
     }
-    if (flag & OC_OBSERVE_FLAG)
+    if (entityHandlerRequest && (flag & OC_OBSERVE_FLAG))
     {
         OIC_LOG(INFO, ES_RH_TAG, "Flag includes OC_OBSERVE_FLAG");