FBRowUpdater incorrectly considers result set with only partial PK updatable

[mrotteveel]

When FBRowUpdater generates its parameter mask, it checks if it found the 'best row identifier', but unfortunately, it fails to reset the boolean used to track that. As a result, if a table has a composite PK, and the prefix of the primary key is included in the query (i.e. first, or first + second, etc), but the suffix is missing (e.g. last, or second last + last, etc.), it will still consider the result set updatable.

Subsequent attempts to update rows through the result may update multiple rows (and refresh row will fail with an exception).

This has been broken since 3.0.0, and no one has reported it, so initially, it will only be fixed in Jaybird 6.

[mrotteveel]

Decided that the (minimal) fix should be backported to Jaybird 5, see #781