fix: address feedback from Delegation Pool pr

Author: juanmardefago

schema.graphql

@@ -948,7 +948,7 @@ type Provision @entity {
   delegatedTokens: BigInt!
   "Total shares of the delegator pool"
   delegatorShares: BigInt!
-  "Exchange rate of of tokens received for each share"
+  "Exchange rate of tokens received for each share"
   delegationExchangeRate: BigDecimal!
   "Ratio between the amount of the indexers own stake over the total usable stake (capped by the delegationRatio)."
   ownStakeRatio: BigDecimal!

src/mappings/horizonStaking.ts

@@ -270,6 +270,9 @@ export function handleTokensToDelegationPoolAdded(event: TokensToDelegationPoolA
     let indexer = Indexer.load(event.params.serviceProvider.toHexString())!
     let provision = createOrLoadProvision(event.params.serviceProvider, event.params.verifier, event.block.timestamp)
     provision.delegatedTokens = provision.delegatedTokens.plus(event.params.tokens)
+    if (provision.delegatorShares != BigInt.fromI32(0)) {
+        provision = updateDelegationExchangeRateForProvision(provision as Provision)
+    }
     provision.save()
 
     indexer.delegatedTokens = indexer.delegatedTokens.plus(event.params.tokens) // this only serves as a general tracker, but the real deal is per provision