This resolves an issue with the modpacks.ch search functionality, in
which a search issued while one is currently in progress won't be made
and the UI won't allow for the search to be made after.
Reproduction Steps:
1. Open the FTB pane in the Add Instance Dialog
2. Perform a search while MMC is still performing the initial search
The search won't be performed, the existing search will have been
aborted, and you are unable to try the search again (without trying a
different search in the meantime).
This was caused by 2 things:
1. A search cannot be re-attempted, and this logic doesn't consider
failures.
2. The failure slot wasn't called when the NetJob was aborted, so
the search would never be performed - but the term would be
stored as if it had (trigering point 1).
I have resolved this by doing 2 things:
1. If the failure slot is called, set a searchState of Failed. Allow
search re-attempts in this case.
2. If there is a present NetJob, abort and reset it. The immediately
continue with the search.
