FIX: basic_properties_clone handle 0-len strings
FIX: basic_properties_clone handle 0-len strings

Properly handle 0-length strings in amqp_basic_properties_clone()

kilinrax/rabbitmq-c,jqk6/rabbitmq-c,jasonmsoft/rabbitmq-c,Haster2004/rabbitmq-c,alanxz/rabbitmq-c,tempbottle/rabbitmq-c,chenwenbin928/rabbitmq-c,sakishum/rabbitmq-c,tempbottle/rabbitmq-c,hjzljp/rabbitmq-c,chenwenbin928/rabbitmq-c,alanxz/rabbitmq-c,jasonmsoft/rabbitmq-c,kilinrax/rabbitmq-c,chenwenbin928/rabbitmq-c,jasonmsoft/rabbitmq-c,sakishum/rabbitmq-c,jasonmsoft/rabbitmq-c,soindy/rabbitmq-c,kilinrax/rabbitmq-c,jqk6/rabbitmq-c,tempbottle/rabbitmq-c,Haster2004/rabbitmq-c,soindy/rabbitmq-c,hjzljp/rabbitmq-c,alanxz/rabbitmq-c,hjzljp/rabbitmq-c,hjzljp/rabbitmq-c,jqk6/rabbitmq-c,jqk6/rabbitmq-c,tempbottle/rabbitmq-c,Haster2004/rabbitmq-c,soindy/rabbitmq-c,sakishum/rabbitmq-c