Panic on invalid unsigned election solution. (#6485)

* Panic on invalid

* Fix return

* Fix refund

substrate/frame/staking/src/lib.rs

@@ -2194,18 +2194,20 @@ decl_module! {
 			size: ElectionSize,
 		) -> DispatchResultWithPostInfo {
 			ensure_none(origin)?;
-			Self::check_and_replace_solution(
+			let adjustments = Self::check_and_replace_solution(
 				winners,
 				compact,
 				ElectionCompute::Unsigned,
 				score,
 				era,
 				size,
-			)
-			// TODO: instead of returning an error, panic. This makes the entire produced block
-			// invalid.
-			// This ensures that block authors will not ever try and submit a solution which is not
-			// an improvement, since they will lose their authoring points/rewards.
+			).expect(
+				"An unsigned solution can only be submitted by validators; A validator should \
+				always produce correct solutions, else this block should not be imported, thus \
+				effectively depriving the validators from their authoring reward. Hence, this panic
+				is expected."
+			);
+			Ok(adjustments)
 		}
 	}
 }