Bug 28885: Skip invalid biblios for OpacBrowseResults

Bug 28885: Skip invalid biblios for OpacBrowseResults

If a record is deleted from Koha, but is for some reason not deleted from the search indexes, OpacBrowseResults can cause an ISE if the deleted record is in the search results for any given item. OpacBrowseResults loops through the search results, and checks if there is a biblionumber, but does *not* check to see if a result was pulled from the database for that biblionumber. It simply assumes the result must exist.

We should be checking to ensure the biblionumber was valid before operating on the biblio object.

Test Plan:
1) Use zebra for searching
2) Disable koha-indexer
3) Enable OpacBrowseResults
4) Perform a search
5) Delete an item in the search results
6) View on of the remaining items in the search results
7) Note the error
8) Apply this patch
9) Restart plack
10) Reload the page
11) The error should be gone!

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>