org-indent: Fix indentation of inline tasks

* lisp/org-indent.el (org-indent--compute-prefixes): Fix indentation
  of inline tasks when `org-inlinetask-show-first-star is non-nil.

Reported-by: Rasmus <rasmus@gmx.us>
<http://lists.gnu.org/archive/html/emacs-orgmode/2017-06/msg00452.html>

lisp/org-indent.el

@@ -142,11 +142,11 @@ useful to make it ever so slightly different."
 	;; Inline tasks line prefixes
 	(aset org-indent--inlinetask-line-prefixes
 	      n
-	      (org-add-props (if (bound-and-true-p org-inlinetask-show-first-star)
-				 (concat org-indent-inlinetask-first-star
-					 (substring heading-prefix 1))
-			       heading-prefix)
-		  nil 'face 'org-indent)))
+	      (cond ((<= n 1) "")
+		    ((bound-and-true-p org-inlinetask-show-first-star)
+		     (concat org-indent-inlinetask-first-star
+			     (substring heading-prefix 1)))
+		    (t (org-add-props heading-prefix nil 'face 'org-indent)))))
       ;; Text line prefixes.
       (aset org-indent--text-line-prefixes
 	    n