Change sqlite3BtreeNext() and sqlite3BtreePrevious() so that they return

SQLITE_DONE if they have already reached the end (or beginning) of the table.
This gives a performance increase and size reduction.

FossilOrigin-Name: e972a3860892022d57b26ec44ce0fbadc61c1ff54b7a10b7e82390db88d323a7

src/vdbe.h

@@ -63,7 +63,7 @@ struct VdbeOp {
 #ifdef SQLITE_ENABLE_CURSOR_HINTS
     Expr *pExpr;           /* Used when p4type is P4_EXPR */
 #endif
-    int (*xAdvance)(BtCursor *, int *);
+    int (*xAdvance)(BtCursor *, int);
   } p4;
 #ifdef SQLITE_ENABLE_EXPLAIN_COMMENTS
   char *zComment;          /* Comment to improve readability */