basic: refactor error handling

Signed-off-by: Alejandro Mery <amery@jpi.io>

basic/token.go

@@ -149,6 +149,8 @@ func (dec *decoder) OnToken(pos lexer.Position, typ parser.TokenType, value stri
 		return nil
 	default:
 		// unacceptable
-		return newErrInvalidToken(t)
+		err := newErrInvalidToken(t)
+		dec.executeFinal()
+		return err
 	}
 }