fix($urlMatcherFactory): make date type fn check .is before running

Closes #1564

src/urlMatcherFactory.js

@@ -588,8 +588,9 @@ function $UrlMatcherFactory() {
  },
  date: {
  encode: function (val) {
- return [
- val.getFullYear(),
+ if (!this.is(val))
+ return undefined;
+ return [ val.getFullYear(),
  ('0' + (val.getMonth() + 1)).slice(-2),
  ('0' + val.getDate()).slice(-2)
  ].join("-");
@@ -600,7 +601,7 @@ function $UrlMatcherFactory() {
  return match ? new Date(match[1], match[2] - 1, match[3]) : undefined;
  },
  is: function(val) { return val instanceof Date && !isNaN(val.valueOf()); },
- equals: function (a, b) { return a.toISOString() === b.toISOString(); },
+ equals: function (a, b) { return this.is(a) && this.is(b) && a.toISOString() === b.toISOString(); },
  pattern: /[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[1-2][0-9]|3[0-1])/,
  capture: /([0-9]{4})-(0[1-9]|1[0-2])-(0[1-9]|[1-2][0-9]|3[0-1])/
  },