[#746] morph/client: Break loop in iterateClients on NeoFS error

There is no need to continue iterating over Neo RPC endpoints in case of
some address-independent error (e.g. NeoFS logic error).

Unwrap and immediately return `neofsError` errors from loop in
`iterateClients`.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/morph/client/multi.go

@@ -94,6 +94,11 @@ func (x *multiClient) iterateClients(f func(*Client) error) error {
 			return nil
 		}
 
+		// we dont need to continue the process after the logical error was encountered
+		if errNeoFS := unwrapNeoFSError(err); errNeoFS != nil {
+			return errNeoFS
+		}
+
 		// set first error once
 		if firstErr == nil {
 			firstErr = err