org-set-effort: Remove extra space in prompt

* lisp/org.el (org-set-effort): Make spacing across different prompt
  cases consistent.  Simplify prompt concatenation.

lisp/org.el

@@ -15701,8 +15701,8 @@ When INCREMENT is non-nil, set the property to the next allowed value."
 	       (t
 		(let (org-completion-use-ido org-completion-use-iswitchb)
 		  (org-completing-read
-		   (concat "Effort " (if (and cur (string-match "\\S-" cur))
-					 (concat "[" cur "]") "")
+		   (concat "Effort" (and cur (string-match "\\S-" cur)
+					 (concat " [" cur "]"))
 			   ": ")
 		   existing nil nil "" nil cur))))))
     (unless (equal (org-entry-get nil prop) val)