Fix uncaught TypeError when this.route is null

[adalinesimonian]

If this.route is null, trying to dereference this.route.fullPath leads to an uncaught TypeError. This error can be easily found when trying to programmatically create an instance of <more-route> when it has no parent, as the preconditions in _identityChanged for setting this.route to null are only that this.name and this.path are both falsy, which is true when the element has just been created with document.createElement('more-route').

Local test results after patch:

Starting Selenium server for local browsers
Selenium server running on port 50417
Web server running on port 50425 and serving from /Users/vartan/Documents/webcomponent-dev/polymer-0.9.x/more-routing
chrome 42                Beginning tests via http://localhost:50425/components/more-routing/generated-index.html?cli_browser_id=0
safari 8.0.6             Beginning tests via http://localhost:50425/components/more-routing/generated-index.html?cli_browser_id=2
chrome 42                Tests passed
safari 8.0.6             Tests passed
firefox 37               Beginning tests via http://localhost:50425/components/more-routing/generated-index.html?cli_browser_id=1
firefox 37               Tests passed
Test run ended with great success

chrome 42 (3/0/0)                       firefox 37 (3/0/0)                    
safari 8.0.6 (3/0/0)