Result set pane not properly cleaned up after "Close All Editors"

[kburtram]

Steps to Reproduce:

1. Open a bunch of SQL editors and run queries.
2. Might need to have one currently executing, like a long running query
3. Run "Close All Editors" from the "Open Editors" view toolbar in the Explorer pane.
    
   Expected: All the windows are closed, all the queries are cancelled, and the Query Results panel is empty.

Actual: The results panel contains the results from one of the queries and appears not be have been cleaned up properly. For example, see below. Also the messages had this error in it Query failed: Invalid attempt to call NextResult when reader is closed..