[coap] fix handling message id 0 (#2104)
[coap] fix handling message id 0 (#2104)


georgecpr/openthread,chshu/openthread,aeliot/openthread,georgecpr/openthread,xiaom-GitHub/openthread,vaas-krish/openthread,fbsder/openthread,georgecpr/openthread,srickardti/openthread,lanyuwen/openthread,chshu/openthread,abtink/openthread,turon/openthread,erja-gp/openthread,aeliot/openthread,pvanhorn/openthread,lanyuwen/openthread,abtink/openthread,librasungirl/openthread,vaas-krish/openthread,LeZhang2016/openthread,fbsder/openthread,gandreello/openthread,srickardti/openthread,bukepo/openthread,erja-gp/openthread,LeZhang2016/openthread,erja-gp/openthread,mszczodrak/openthread,LeZhang2016/openthread,bukepo/openthread,lanyuwen/openthread,vaas-krish/openthread,mszczodrak/openthread,gandreello/openthread,jwhui/openthread,turon/openthread,gandreello/openthread,jwhui/openthread,srickardti/openthread,erja-gp/openthread,pvanhorn/openthread,xiaom-GitHub/openthread,abtink/openthread,chshu/openthread,librasungirl/openthread,georgecpr/openthread,LeZhang2016/openthread,gandreello/openthread,vaas-krish/openthread,fbsder/openthread,lanyuwen/openthread,lanyuwen/openthread,turon/openthread,fbsder/openthread,mszczodrak/openthread,openthread/openthread,aeliot/openthread,pvanhorn/openthread,chshu/openthread,bukepo/openthread,georgecpr/openthread,xiaom-GitHub/openthread,xiaom-GitHub/openthread,chshu/openthread,abtink/openthread,jwhui/openthread,erja-gp/openthread,aeliot/openthread,openthread/openthread,vaas-krish/openthread,mszczodrak/openthread,openthread/openthread,xiaom-GitHub/openthread,gandreello/openthread,chshu/openthread,srickardti/openthread,gandreello/openthread,aeliot/openthread,pvanhorn/openthread,jwhui/openthread,turon/openthread,bukepo/openthread,librasungirl/openthread,librasungirl/openthread,georgecpr/openthread,LeZhang2016/openthread,vaas-krish/openthread,mszczodrak/openthread,mszczodrak/openthread,erja-gp/openthread,LeZhang2016/openthread,xiaom-GitHub/openthread,fbsder/openthread,lanyuwen/openthread,aeliot/openthread,openthread/openthread,fbsder/openthread,pvanhorn/openthread,pvanhorn/openthread