Add missing Org Mode state trigger for empty keyword

Then a project is set on hold, the HOLD keyword is added.  When reverting the
hold state, projects go back to not having a keyword.  In this case, the HOLD
tag remains, because the old trigger definition was missing a case for the empty
keyword.  This is now fixed.

init.el

@@ -765,7 +765,8 @@ With given ARG, display files in `db/important-document-path’."
                   ("READ" ("READ" . t) ("HOLD") ("WAIT"))
                   ("GOTO" ("DATE" . t) ("HOLD") ("WAIT"))
                   ("CONT" ("HOLD") ("WAIT"))
-                  ("ATTN" ("HOLD") ("WAIT")))
+                  ("ATTN" ("HOLD") ("WAIT"))
+                  ("" ("HOLD") ("WAIT") ("DATE") ("READ")))
 
                 org-tag-alist
                 '((:startgroup . nil)