Bug 29697: tracklinks should not explode on invalid marc record

Bug 29697: tracklinks should not explode on invalid marc record

Caught by t/db_dependent/www/regressions.t

    #   Failed test '404 for itemnumber containing different URI'
    #   at t/db_dependent/www/regressions.t line 124.
    #          got: '500'
    #     expected: '404'

    #   Failed test '302 for itemnumber with matching URI'
    #   at t/db_dependent/www/regressions.t line 126.
    #          got: '500'
    #     expected: '302'

    #   Failed test '404 for itemnumber containing different URI'
    #   at t/db_dependent/www/regressions.t line 139.
    #          got: '500'
    #     expected: '404'

    #   Failed test '302 for itemnumber with matching URI'
    #   at t/db_dependent/www/regressions.t line 141.
    #          got: '500'
    #     expected: '302'
    # Looks like you failed 4 tests of 36.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>