Wrap around the Q score index (#935)

## Describe your changes

Wrap around q score sample index if it overflows

pallets/ocex/src/lmp.rs

@@ -299,10 +299,7 @@ pub fn store_q_score_and_uptime(
 		Some(encoded_q_scores_map) => {
 			let mut map = BTreeMap::<u16, Decimal>::decode(&mut &encoded_q_scores_map[..])
 				.map_err(|_| "Unable to decode decimal")?;
-			if map.insert(index, score).is_some() {
-				log::error!(target:"ocex","Overwriting q score with index: {:?}, epoch: {:?}, main: {:?}, market: {:?}",index,epoch,main,trading_pair);
-				return Err("Overwriting q score");
-			}
+			map.insert(index, score); // We overwrite on wrapping around
 			log::info!(target: "ocex","Writing Q score and uptime for main: {:?}",main);
 			state.insert(key, map.encode());
 		},

pallets/ocex/src/validator.rs

@@ -749,7 +749,8 @@ impl<T: Config> Pallet<T> {
 		current_on_chain_epoch: u16,
 	) -> Result<(), &'static str> {
 		let mut config = get_lmp_config(state, current_on_chain_epoch)?;
-		let next_index = config.index.saturating_add(1);
+		// We wrap around the index if we overflow
+		let next_index = config.index.checked_add(1).unwrap_or(0);
 		for (main, score) in scores {
 			store_q_score_and_uptime(
 				state,