Fix state.show_states when sls file missing in top file

[Ch3LL]

What does this PR do?

When a sls file is defined in a top.sls file that is missing a TypeError was raised when using state.show_states. This PR ensures we do not stacktrace and handle this situation

What issues does this PR fix or reference?

#54758

Previous Behavior

Passed invalid arguments: string indices must be integers.

Usage:

    Returns the list of states that will be applied on highstate.

    CLI Example:

    .. code-block:: bash

        salt '*' state.show_states

    .. versionadded:: 2019.2.0

New Behavior

local:
       - No matching sls found for 'cloud' in env 'base'

Tests written?

Yes

Commits signed with GPG?

Yes

[Ch3LL]

re-run full all