DDSIRTP26 — Handling of non-existent cache changes in logical action

In the version 2.3 specs, a gap is inserted in case a cache change isn't available in the history cache. In the 2.5 specs, only the highest previously sent sequence number is taken into account to determine if agap should be inserted.
The shown logical actions will fail if the cache change with a_change_seq_num can't be located in the cache. in which case a gap should be inserted as well as in the 2.3 specs. Considering the explanation given for sending a gap because of the HISTORY QoS set to KEEP_LAST in the last paragraph on page 82, one should definitely consider the situation that a cache change is missing.