Return error instead of panicing.

Author: davidblewett

src/consumer/stream_consumer.rs

@@ -207,11 +207,20 @@ where
     fn from_config_and_context(config: &ClientConfig, context: C) -> KafkaResult<Self> {
         let native_config = config.create_native_config()?;
         let poll_interval = {
-            let millis: u64 = native_config
-                .get("max.poll.interval.ms")?
-                .parse()
-                .expect("librdkafka validated config value is valid u64");
-            Duration::from_millis(millis)
+            let millis = native_config.get("max.poll.interval.ms")?;
+            match millis.parse() {
+                Ok(millis) => Duration::from_millis(millis),
+                Err(e) => {
+                    println!("Config string: '{}'", millis);
+                    println!("Error: '{}'", e);
+                    return Err(KafkaError::ClientConfig(
+                        RDKafkaConfRes::RD_KAFKA_CONF_INVALID,
+                        "max.poll.interval.ms".to_string(),
+                        format!("Invalid integer: {}", e),
+                        millis,
+                    ));
+                }
+            }
         };
 
         let base = Arc::new(BaseConsumer::new(config, native_config, context)?);