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

Previously, when an object has keys which are not of type string, the `filter` would throw an exception for trying to call `charAt`, which is not defined on a none-string type.

This commit checks whether `charAt` is defined before calling it.

Closes #15644

Author: frederikprijck

src/ng/filter/filter.js

@@ -226,7 +226,7 @@ function deepCompare(actual, expected, comparator, anyPropertyKey, matchAgainstA
       var key;
       if (matchAgainstAnyProp) {
         for (key in actual) {
-          if ((key.charAt(0) !== '$') && deepCompare(actual[key], expected, comparator, anyPropertyKey, true)) {
+          if (key.charAt && (key.charAt(0) !== '$') && deepCompare(actual[key], expected, comparator, anyPropertyKey, true)) {
             return true;
           }
         }