Check if context is dictionary and process further

Sorry, I was using this pull request for the first time and got confused. 

Anyways, I was having this issue: ValueError: dictionary update sequence element #0 has length 0; 2 is required at debug_toolbar.panels.templates.panel in _request_context__init__. 

It looks like it's complaining that request context consists an object. When rendering to response I always pass variables into context so that I can use them in templates. Isn't that a common Django practice?

So this fix just checks if context is dictionary and processes further. 

Here's the stacktrace: 
![screenshot at nov 05 22-01-46](https://cloud.githubusercontent.com/assets/2887118/4930246/53bbd406-6561-11e4-9417-d354a979cf02.png)