do not try to process an empty message
do not try to process an empty message

When no message is complete and no error occurred,
an empty message is returned.

JGrothoff/open62541,open62541/open62541,StalderT/open62541,jpfr/open62541,open62541/open62541,JGrothoff/open62541,JGrothoff/open62541,StalderT/open62541,jpfr/open62541,StalderT/open62541,jpfr/open62541,StalderT/open62541,jpfr/open62541,open62541/open62541,open62541/open62541,JGrothoff/open62541