getLinkTarget.xql fails if window title not foud for mei:work

Created by: bwbohl

https://github.com/Edirom/Edirom-Online/blob/914ccfd7dc9f3f10cbbf9ab9640980e764dc2f04/add/data/xql/getLinkTarget.xql#L170

e.g. in MEI 4.0.1 work does no longer contain titleStmt

mentioned in commit 8accbac0

mentioned in commit 97bc2f56

mentioned in commit 6ce89862

mentioned in commit 905e1078

mentioned in commit 5c01b848