Fix CUSTOM_ID search

* lisp/org.el (org-link-search): Avoid false positives when searching
  CUSTOM_ID property.

* testing/lisp/test-org.el (test-org/custom-id): Add test.

lisp/org.el

@@ -10999,19 +10999,10 @@ variable."
      ;; First check if there are any special search functions
      ((run-hook-with-args-until-success 'org-execute-file-search-functions s))
      ;; Now try the builtin stuff
-     ((and (equal (string-to-char s0) ?#)
+     ((and (eq (aref s0 0) ?#)
 	   (> (length s0) 1)
-	   (save-excursion
-	     (goto-char (point-min))
-	     (and
-	      (re-search-forward
-	       (concat "^[ \t]*:CUSTOM_ID:[ \t]+"
-		       (regexp-quote (substring s0 1)) "[ \t]*$") nil t)
-	      (setq type 'dedicated
-		    pos (match-beginning 0))))
-	   ;; There is an exact target for this
-	   (goto-char pos)
-	   (org-back-to-heading t)))
+	   (let ((match (org-find-property "CUSTOM_ID" (substring s0 1))))
+	     (and match (goto-char match) (setf type 'dedicated)))))
      ((save-excursion
 	(goto-char (point-min))
 	(and

testing/lisp/test-org.el

@@ -1313,6 +1313,13 @@
        "* H1\n:PROPERTIES:\n:CUSTOM_ID: custom\n:END:\n* H2\n[[#custom]]"
      (goto-char (point-max))
      (org-open-at-point)
+     (org-looking-at-p "\\* H1")))
+  ;; Ignore false positives.
+  (should-not
+   (org-test-with-temp-text
+       "* H1\n:DRAWER:\n:CUSTOM_ID: custom\n:END:\n* H2\n[[#custom]]<point>"
+     (goto-char (point-max))
+     (let (org-link-search-must-match-exact-headline) (org-open-at-point))
      (org-looking-at-p "\\* H1"))))
 
 ;;;; Fuzzy Links