`IndexError: list index out of range` for stored procedures

I get a crash when trying to run a built-in stored procedure:
```
HRDB> exec sp_spaceused;
Traceback (most recent call last):
File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
"__main__", fname, loader, pkg_name)
File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
exec code in run_globals
File "/home/eric/.virtualenvs/awscli/lib/python2.7/site-packages/mssqlcli/main.py", line 117, in
main()
File "/home/eric/.virtualenvs/awscli/lib/python2.7/site-packages/mssqlcli/main.py", line 110, in main
run_cli_with(mssqlcli_options)
File "/home/eric/.virtualenvs/awscli/lib/python2.7/site-packages/mssqlcli/main.py", line 55, in run_cli_with
mssqlcli.run()
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssql_cli.py", line 440, in run
self.execute_query(text)
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssql_cli.py", line 365, in execute_query
output = self._execute_interactive_command(text)
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssql_cli.py", line 321, in _execute_interactive_command
output, query = self._evaluate_command(text)
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssql_cli.py", line 548, in _evaluate_command
self.mssqlcliclient_main.execute_query(text):
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssqlcliclient.py", line 112, in execute_query
in self._execute_query(single_query):
File "/home/eric/.virtualenvs/awscli/local/lib/python2.7/site-packages/mssqlcli/mssqlcliclient.py", line 146, in _execute_query
= query_messages[result_set_summary.request_id].message if query_messages else u''
IndexError: list index out of range
```

Reproduce the failure with `exec sp_spaceused;` in the mssql-cli client, then inspect `mssqlcliclient.py`, especially `_execute_query` around line 146 and the query execution path shown in the traceback. Done means built-in stored procedures no longer produce `IndexError: list index out of range` and their output or messages are handled without a crash.

Written by the indexing model from the issue text.