[dataset] check if dataset is present in otDatasetIsCommissioned (#4426)
[dataset] check if dataset is present in otDatasetIsCommissioned (#4426)

otDatasetIsCommissioned API first reads out the Active Dataset from
settings (i.e. non-volatile storage). However, the existing
implementation does not check if the Active Dataset is actually
present, as indicated by OT_ERROR_NOT_FOUND.

This commit adds a necessary check and returns false if the Active
Dataset is not present.
chshu/openthread,openthread/openthread,openthread/openthread,lanyuwen/openthread,bukepo/openthread,chshu/openthread,abtink/openthread,librasungirl/openthread,lanyuwen/openthread,srickardti/openthread,chshu/openthread,abtink/openthread,bukepo/openthread,jwhui/openthread,lanyuwen/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,chshu/openthread,srickardti/openthread,srickardti/openthread,jwhui/openthread,chshu/openthread,abtink/openthread,chshu/openthread,librasungirl/openthread,lanyuwen/openthread,openthread/openthread,jwhui/openthread,abtink/openthread,librasungirl/openthread,librasungirl/openthread,lanyuwen/openthread,bukepo/openthread,bukepo/openthread,lanyuwen/openthread