Handle 'show' gracefully when plugin not installed

[techman83]

Not installed

D:\>ckan show AJE

Unhandled Exception: System.Collections.Generic.KeyNotFoundException: The given
key was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at CKAN.MainClass.Show(ShowOptions options)
   at CKAN.MainClass.Main(String[] args)

Installed

D:\>ckan install AJE
AJE:

    * Using AJE-1.5.zip (cached)
    * Installing AJE
ModuleManager 2.2.0 already installed, skipping bundled version 2.3.5

Done!

D:\>ckan show AJE
Advanced Jet Engine (AJE) version 1.5

[pjf]

Thank you, and agree! Added to first release milestone. :)

[pjf]

@techman83 : Fixed in #51! If you fancy glancing over it and merging if it looks good, that would be grand. :)

(Not sure why the unified diff looks so funny, the split diff is much clearer.)

[techman83]

@Wizarth appears to have beaten me to it - need to stop spending so much time in the physical world! :)