Rlp decode returns Result (#8527)

rlp::decode returns Result

Make a best effort to handle decoding errors gracefully throughout the code, using `expect` where the value is guaranteed to be valid (and in other places where it makes sense).

whisper/src/message.rs

@@ -446,7 +446,7 @@ mod tests {
 		};
 
 		let encoded = ::rlp::encode(&envelope);
-		let decoded = ::rlp::decode(&encoded);
+		let decoded = ::rlp::decode(&encoded).expect("failure decoding Envelope");
 
 		assert_eq!(envelope, decoded)
 	}
@@ -462,7 +462,7 @@ mod tests {
 		};
 
 		let encoded = ::rlp::encode(&envelope);
-		let decoded = ::rlp::decode(&encoded);
+		let decoded = ::rlp::decode(&encoded).expect("failure decoding Envelope");
 
 		assert_eq!(envelope, decoded)
 	}