consumer: more robust handling of message offsets
consumer: more robust handling of message offsets

- Only skip messages before the requested offset at the beginning of a set
- Error if we don't receive any legitimate messages in the set.

VividCortex/sarama,kmiku7/sarama,uovobw/sarama,pronix/sarama,LastManStanding/sarama,uovobw/sarama,jepst/sarama,scalingdata/sarama,LastManStanding/sarama,remerge/sarama,scalingdata/sarama,rafrombrc/sarama,jimmykuo/sarama,DataDog/sarama,crast/sarama,aybabtme/sarama,betable/sarama,winlinvip/sarama,cep21/sarama,gyroscope-innovations/legacy_sarama,Shopify/sarama,raisemarketplace/sarama,vrischmann/sarama,rafrombrc/sarama,HelixEducation/sarama,kmiku7/sarama,HelixEducation/sarama,kraveio/sarama,Neuw84/sarama,gyroscope-innovations/legacy_sarama,VividCortex/sarama,yangfan876/sarama,DataDog/sarama,Shopify/sarama,cep21/sarama,Neuw84/sarama,raisemarketplace/sarama,betable/sarama,pronix/sarama,jimmykuo/sarama,aybabtme/sarama,jepst/sarama,kraveio/sarama,crast/sarama,vrischmann/sarama,mailgun/sarama,yangfan876/sarama,remerge/sarama,winlinvip/sarama,mailgun/sarama