If we decode Exist bit as "1" but we are at the end of the message, and
all the Next items we'd read are expected to be possibly NULL, then swap
the Exist bit in the decoded structure as "0" in order to tell the
decoder user that the related information structure is actually unset,
as if "0" was received.
Related: SYS#5552
Related: OS#4955
Related: OS#5020
Change-Id: I38602e4b680ed87297c7e440691a494c07cad446