Bug 10879: OverDrive should check for OverDriveLibraryID before performing search

Bug 10879: OverDrive should check for OverDriveLibraryID before performing search

This patch modifies the OPAC search results template to check for three
populated system preferences before performing an OverDrive search:
OverDriveLibraryID, OverDriveClientKey, and OverDriveClientSecret.
Previously OverDriveLibraryID was not checked, but without it the
interface reports an error performing the search.

To test you must have credentials for the OverDrive API as defined
in OverDriveClientKey, OverDriveClientSecret, and OverDriveLibraryID
system preferences.

 - With OverDriveLibraryID defined, the catalog search results page in
   the OPAC should show a link to results in the library's OverDrive
   collection.

 - With no value in the OverDriveLibraryID preference the catalog
   search page should not show any message about an OverDrive
   collection.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>