Don't measure encoding of too small region when adjusting chunk start

and fix passing of elements to tune in vlf-occur.

vlf-base.el

@@ -308,8 +308,10 @@ Return number of bytes moved back for proper decoding."
                        (not (zerop safe-start)))
                 (< shift 3)
                 (let ((diff (- chunk-size
-                               (vlf-tune-encode-length position
-                                                       (point-max)))))
+                               (length
+                                (encode-coding-region
+                                 position (point-max)
+                                 buffer-file-coding-system t)))))
                   (if strict
                       (not (zerop diff))
                     (or (< diff -3) (< 0 diff)))))

vlf-occur.el

@@ -202,7 +202,7 @@ Prematurely ending indexing will still show what's found so far."
          (time (float-time))
          (tune-types (let ((base '(:insert :encode)))
                        (if is-hexl
-                           (nconc '(:hexl :dehexlify) base)
+                           (append '(:hexl :dehexlify) base)
                          base)))
          (reporter (make-progress-reporter
                     (concat "Building index for " regexp "...")