bug fix, modify precedence.

Author: wanghao1891

lib/mongoosastic.js

@@ -552,7 +552,7 @@ module.exports = function Mongoosastic(schema, options) {
                     if (theVal) {
                         final[path] = theVal;
                     } else {
-                        if(origCondition.$or[0]) {
+                        if(origCondition.$or && origCondition.$or[0]) {
                             theVal = origCondition.$or[0][path];
                             if(theVal) {
                                 final[path] = theVal;