Invalid stored offset makes consumer panic

[horkhe]

If an offset stored for a topic partition is out of partition bounds then Kafka-Pixy panics on consumption attempt:

panic: </smartConsumer[1]/group-1[0]/test.1:0[0]> failed to start partition consumer: offset=1152, err=(kafka server: The requested offset is outside the range of offsets maintained by the server for the given topic/partition.)

goroutine 704 [running]:
panic(0x4ff6a0, 0xc820680240)
    /usr/local/go/src/runtime/panic.go:464 +0x3e6
github.com/mailgun/kafka-pixy/consumer.(*exclusiveConsumer).run(0xc82051e6c0)
    /Users/maximvladimirsky/workspace/goworld/src/github.com/mailgun/kafka-pixy/consumer/smart_consumer.go:292 +0x6d4
github.com/mailgun/kafka-pixy/consumer.(*exclusiveConsumer).(github.com/mailgun/kafka-pixy/consumer.run)-fm()
    /Users/maximvladimirsky/workspace/goworld/src/github.com/mailgun/kafka-pixy/consumer/smart_consumer.go:260 +0x20
github.com/mailgun/kafka-pixy/consumer.spawn.func1(0xc82051e738, 0xc82047f6d0)
    /Users/maximvladimirsky/workspace/goworld/src/github.com/mailgun/kafka-pixy/consumer/utils.go:16 +0x44
created by github.com/mailgun/kafka-pixy/consumer.spawn
    /Users/maximvladimirsky/workspace/goworld/src/github.com/mailgun/kafka-pixy/consumer/utils.go:17 +0x56
exit status 2
FAIL    github.com/mailgun/kafka-pixy/consumer  7.868s

That can happen when consumption of a topic stopped for period of time greater than the topic retention period.