Add the OP_FinishSeek opcode which completes an OP_DeferredSeek if the seek

has not already completed.  Also add the sqlite3WhereUsesDeferredSeek()
interface to the query planner.  The UPDATE implementation adds an
OP_FinishSeek before running the final OP_Insert if one is needed.
Ticket [ec8abb025e78f40c] and also an assertion fault reported by Yongheng.

FossilOrigin-Name: 21ef6e99331210b80fa7c71b4f02e8f768a748d01aef884368af2f6b51a067e0

src/whereInt.h

@@ -459,6 +459,7 @@ struct WhereInfo {
   i8 nOBSat;                /* Number of ORDER BY terms satisfied by indices */
   u8 sorted;                /* True if really sorted (not just grouped) */
   u8 eOnePass;              /* ONEPASS_OFF, or _SINGLE, or _MULTI */
+  u8 bDeferredSeek;         /* Uses OP_DeferredSeek */
   u8 untestedTerms;         /* Not all WHERE terms resolved by outer loop */
   u8 eDistinct;             /* One of the WHERE_DISTINCT_* values */
   u8 bOrderedInnerLoop;     /* True if only the inner-most loop is ordered */