org.el (org-shiftcontrolup, org-shiftcontroldown): Ignore `org-support-shift-select' when point is on a clock log

* org.el (org-shiftcontrolup, org-shiftcontroldown): When
`org-support-shift-select' is not `nil', let-bind it to nil
if point is on a clock log.  Otherwise throw an error.

lisp/org.el

@@ -20036,21 +20036,19 @@ Depending on context, this does one of the following:
   "Change timestamps synchronously up in CLOCK log lines.
 Optional argument N tells to change by that many units."
   (interactive "P")
-  (cond ((and (not org-support-shift-select)
-	      (org-at-clock-log-p)
-	      (org-at-timestamp-p t))
-	 (org-clock-timestamps-up n))
-	(t (org-shiftselect-error))))
+  (if (and (org-at-clock-log-p) (org-at-timestamp-p t))
+      (let (org-support-shift-select)
+	(org-clock-timestamps-up n))
+    (user-error "Not at a clock log")))
 
 (defun org-shiftcontroldown (&optional n)
   "Change timestamps synchronously down in CLOCK log lines.
 Optional argument N tells to change by that many units."
   (interactive "P")
-  (cond ((and (not org-support-shift-select)
-	      (org-at-clock-log-p)
-	      (org-at-timestamp-p t))
-	 (org-clock-timestamps-down n))
-	(t (org-shiftselect-error))))
+  (if (and (org-at-clock-log-p) (org-at-timestamp-p t))
+      (let (org-support-shift-select)
+	(org-clock-timestamps-down n))
+    (user-error "Not at a clock log")))
 
 (defun org-ctrl-c-ret ()
   "Call `org-table-hline-and-move' or `org-insert-heading' dep. on context."