More descriptive error message when invalid slot duration is used (#6430)

* Initial commit

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* Errors if slot_duration is zero

* Errors if slot_duration is zero

* Revert "Errors if slot_duration is zero"

This reverts commit a9e9820e124571f73d3e498e969a74d01fd3fe96.

* Update client/consensus/slots/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/consensus/slots/src/lib.rs

@@ -455,7 +455,7 @@ impl<T: Clone> SlotDuration<T> {
 		CB: FnOnce(ApiRef<C::Api>, &BlockId<B>) -> sp_blockchain::Result<T>,
 		T: SlotData + Encode + Decode + Debug,
 	{
-		match client.get_aux(T::SLOT_KEY)? {
+		let slot_duration = match client.get_aux(T::SLOT_KEY)? {
 			Some(v) => <T as codec::Decode>::decode(&mut &v[..])
 				.map(SlotDuration)
 				.map_err(|_| {
@@ -479,7 +479,15 @@ impl<T: Clone> SlotDuration<T> {
 
 				Ok(SlotDuration(genesis_slot_duration))
 			}
+		}?;
+
+		if slot_duration.slot_duration() == 0 {
+			return Err(sp_blockchain::Error::Msg(
+				"Invalid value for slot_duration: the value must be greater than 0.".into(),
+			))
 		}
+
+		Ok(slot_duration)
 	}
 
 	/// Returns slot data value.