Fix tealdbg Accounts array (algorand#1872)

Currently the `Accounts` array is not displayed properly in tealdbg. The debugger does not account for the special case that index 0 of the `Accounts` array is always the sender. This means that if the ForeignAccounts txn field contains `n` accounts, the `Accounts` array in tealdbg contains the sender's account followed by `n-1` of the ForeignAccounts. The last account never gets displayed.

This PR fixes this problem by making tealdbg aware that the `Accounts` array has 1 more member (the sender's account) than `len(txn.Accounts)`. As a consequence of this, the sender's account will always appear at index 0 of the `Accounts` array in the debugger, even when the transaction's ForeignAccounts array is empty. This aligns with the behavior of the TEAL op `txna Accounts 0` always returning the sender's address, even in stateless TEAL.

cmd/tealdbg/cdtState.go

@@ -721,7 +721,7 @@ func makeTxnImpl(txn *transactions.Transaction, groupIndex int, preview bool) (d
 		var length int
 		switch logic.TxnField(fieldIdx) {
 		case logic.Accounts:
-			length = len(txn.Accounts)
+			length = len(txn.Accounts) + 1
 		case logic.ApplicationArgs:
 			length = len(txn.ApplicationArgs)
 		}
@@ -765,7 +765,7 @@ func makeTxnArrayField(s *cdtState, groupIndex int, fieldIdx int) (desc []cdt.Ru
 		var length int
 		switch logic.TxnField(fieldIdx) {
 		case logic.Accounts:
-			length = len(txn.Accounts)
+			length = len(txn.Accounts) + 1
 		case logic.ApplicationArgs:
 			length = len(txn.ApplicationArgs)
 		}