Fix client crash caused by observe cancellation with sequence No 1.

Fix client crash caused by observe cancellation with sequence No 1.

1. Added support for sequence number starting from 1.
2. When sequence number is 1, client treats it as a normal response
rather than de-registration response.
3. Correct default sequence number value to be valid.

JIRA Issue: https://jira.iotivity.org/browse/IOT-1195

Change-Id: I2ce68d70ff5f8f0cce98234a7dbda566b8085a61
Signed-off-by: Ziran Sun <ziran.sun@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/9519
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Mushfiqul Islam <i.mushfiq@samsung.com>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>