org-capture: Fix clipboard history with %^C or %^L place holders

* lisp/org-capture.el (org-capture--clipboards): New variable.
(org-capture-fill-template): Use new variable.

Reported-by: Allen Li <darkfeline@felesatra.moe>
<http://permalink.gmane.org/gmane.emacs.orgmode/113020>

lisp/org-capture.el

@@ -1549,6 +1549,9 @@ Lisp programs can force the template by setting KEYS to a string."
 	       '(("C" "Customize org-capture-templates")
 		 ("q" "Abort"))))))
 
+(defvar org-capture--clipboards nil
+  "List various clipboards values.")
+
 (defun org-capture-fill-template (&optional template initial annotation)
   "Fill a template and return the filled template as a string.
 The template may still contain \"%?\" for cursor positioning."
@@ -1597,12 +1600,13 @@ The template may still contain \"%?\" for cursor positioning."
 		   org-clock-heading)))
 	 (v-f (or (org-capture-get :original-file-nondirectory) ""))
 	 (v-F (or (org-capture-get :original-file) ""))
-	 (clipboards (delq nil
-			   (list v-i
-				 (org-get-x-clipboard 'PRIMARY)
-				 (org-get-x-clipboard 'CLIPBOARD)
-				 (org-get-x-clipboard 'SECONDARY)
-				 v-c))))
+	 (org-capture--clipboards
+	  (delq nil
+		(list v-i
+		      (org-get-x-clipboard 'PRIMARY)
+		      (org-get-x-clipboard 'CLIPBOARD)
+		      (org-get-x-clipboard 'SECONDARY)
+		      v-c))))
 
     (setq org-store-link-plist (plist-put org-store-link-plist :annotation v-a))
     (setq org-store-link-plist (plist-put org-store-link-plist :initial v-i))
@@ -1742,24 +1746,21 @@ The template may still contain \"%?\" for cursor positioning."
 			 (and (org-at-heading-p)
 			      (let ((org-ignore-region t))
 				(org-set-tags nil 'align))))))
-		    ("C"
-		     (cond
-		      ((= (length clipboards) 1) (insert (car clipboards)))
-		      ((> (length clipboards) 1)
-		       (insert (read-string "Clipboard/kill value: "
-					    (car clipboards)
-					    '(clipboards . 1)
-					    (car clipboards))))))
-		    ("L"
-		     (cond ((= (length clipboards) 1)
-			    (org-insert-link 0 (car clipboards)))
-			   ((> (length clipboards) 1)
-			    (org-insert-link
-			     0
-			     (read-string "Clipboard/kill value: "
-					  (car clipboards)
-					  '(clipboards . 1)
-					  (car clipboards))))))
+		    ((or "C" "L")
+		     (let ((insert-fun (if (equal key "C") #'insert
+					 (lambda (s) (org-insert-link 0 s))))
+			   (first-value (car org-capture--clipboards)))
+		       (pcase (length org-capture--clipboards)
+			 (nil nil)
+			 (`(,value) (funcall insert-fun value))
+			 (`(,first-value . ,_)
+			  (funcall insert-fun
+				   (read-string "Clipboard/kill value: "
+						first-value
+						'org-capture--clipboards
+						first-value)))
+			 (_ (error "Invalid `org-capture--clipboards' value: %S"
+				   org-capture--clipboards)))))
 		    ("p" (org-set-property prompt nil))
 		    ((guard key)
 		     ;; These are the date/time related ones.