Correctly raise a parse exception with a missing loop body (#1585)

lib/parse.js

@@ -787,6 +787,8 @@ function parse($TEXT, options) {
         return function() {
             var start = S.token;
             var expr = parser();
+            if (!expr) croak("Expected expression");
+
             var end = prev();
             expr.start = start;
             expr.end = end;