fix assertion failure when database is specified with no URL path (#13164)
fix assertion failure when database is specified with no URL path (#13164)

(e.g. `/_db/system`). In this case, in maintainer mode an assertion
failure was triggered, but it didn't have any effect in non-maintainer
mode.
arangodb/arangodb,Simran-B/arangodb,arangodb/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,graetzer/arangodb,Simran-B/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,graetzer/arangodb,Simran-B/arangodb,Simran-B/arangodb,Simran-B/arangodb,graetzer/arangodb,arangodb/arangodb,Simran-B/arangodb,graetzer/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,Simran-B/arangodb,Simran-B/arangodb,graetzer/arangodb,graetzer/arangodb,Simran-B/arangodb,Simran-B/arangodb,arangodb/arangodb,graetzer/arangodb,arangodb/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,wiltonlazary/arangodb