org-ts-regexp0: Fix matching timestamps with no day name

* lisp/org.el (org-ts-regexp1): Update regexp to match strings like
"2022-04-29 02:00" with no day name.

Reported-by: Russell Adams <RLAdams@adamsinfoserv.com>
Link: https://orgmode.org/list/87zgk8tc17.fsf@localhost

lisp/org.el

@@ -436,7 +436,7 @@ FULL is given."
 This one does not require the space after the date, so it can be used
 on a string that terminates immediately after the date.")
 
-(defconst org-ts-regexp1 "\\(\\([0-9]\\{4\\}\\)-\\([0-9]\\{2\\}\\)-\\([0-9]\\{2\\}\\) *\\([^]+0-9>\r\n -]*\\)\\( \\([0-9]\\{1,2\\}\\):\\([0-9]\\{2\\}\\)\\)?\\)"
+(defconst org-ts-regexp1 "\\(\\([0-9]\\{4\\}\\)-\\([0-9]\\{2\\}\\)-\\([0-9]\\{2\\}\\)\\(?: *\\([^]+0-9>\r\n -]+\\)\\)?\\( \\([0-9]\\{1,2\\}\\):\\([0-9]\\{2\\}\\)\\)?\\)"
   "Regular expression matching time strings for analysis.")
 
 (defconst org-ts-regexp2 (concat "<" org-ts-regexp1 "[^>\n]\\{0,16\\}>")