fixup! fix(filter): Don't throw key.charAt is not a function when object's keys are not of type string.

Author: frederikprijck

src/ng/filter/filter.js

@@ -226,6 +226,8 @@ function deepCompare(actual, expected, comparator, anyPropertyKey, matchAgainstA
       var key;
       if (matchAgainstAnyProp) {
         for (key in actual) {
+          // Under certain, rare, circumstances, key may not be a string and `charAt` will be undefined
+          // See: https://github.com/angular/angular.js/issues/15644
           if (key.charAt && (key.charAt(0) !== '$') && deepCompare(actual[key], expected, comparator, anyPropertyKey, true)) {
             return true;
           }