some qti questions that are converted don't have an identifier
like they're supposed to. This allows those questions to still
be processed without causing an error
refs #5546
Change-Id: I2bc931a65095fca2e73beaaf578f99037e5e09e3
Reviewed-on: https://gerrit.instructure.com/6400
Tested-by: Hudson <hudson@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>