improve error marker placement (#1644)

For AST_UnaryPrefix, points to the operator rather than end of expression.

lib/parse.js

@@ -1457,7 +1457,7 @@ function parse($TEXT, options) {
 
     function make_unary(ctor, op, expr) {
         if ((op == "++" || op == "--") && !is_assignable(expr))
-            croak("Invalid use of " + op + " operator");
+            croak("Invalid use of " + op + " operator", null, ctor === AST_UnaryPrefix ? expr.start.col - 1 : null);
         return new ctor({ operator: op, expression: expr });
     };