Fix bug introduced in PR#134 that prevented the uploadCSV button from…

… ever getting enabled. That bug was caused because it did not insert the "empty dropdown value" to the dropdown list, which resulted in preventing the event `dropdownSelectionChanged` from being called when a single item was in the dropdown list. This would prevent disbursements instructions from being added.

src/components/DisbursementDetails/index.tsx

@@ -328,6 +328,7 @@ export const DisbursementDetails: React.FC<DisbursementDetailsProps> = ({
           value={details.asset.id}
           disabled={isWalletAssetsFetching || !details.wallet.id}
         >
+          {renderDropdownDefault(isWalletAssetsFetching)}
           {walletAssets
             ?.filter((wa: ApiAsset) => {
               // Check for the default native asset