fix(org): don't optimize already-open agenda buffers

`org-map-entries` uses `org-get-agenda-file-buffer` to visit agenda
files, and Doom optimizes the latter to open those org buffers in a
limited capacity (since buffers opened this way are rarely visible, and
full initialization of them is very expensive), deferring their
initialization until the user interactively switches to the buffer
later.

However, if an agenda buffer has already been visited, opening it with
`org-get-agenda-file-buffer` with all these disabled initializations
could have unpredictable effects on whatever the user is doing in their
`org-map-entries` call. Since these optimizations aren't needed for
agenda buffers that already exist, I'll no-op `+org--restart-mode-h` in
those cases.

Fix: #7979

modules/lang/org/config.el

@@ -799,19 +799,22 @@ via an indirect buffer."
     `org-mode' when they're switched to so they can grow up to be fully-fledged
     org-mode buffers."
     :around #'org-get-agenda-file-buffer
-    (let ((recentf-exclude (list (lambda (_file) t)))
-          (doom-inhibit-large-file-detection t)
-          org-startup-indented
-          org-startup-folded
-          vc-handled-backends
-          org-mode-hook
-          find-file-hook)
-      (let ((buf (funcall fn file)))
-        (if buf
-         (with-current-buffer buf
-            (add-hook 'doom-switch-buffer-hook #'+org--restart-mode-h
-                      nil 'local)))
-       buf)))
+    (if-let (buf (org-find-base-buffer-visiting file))
+        buf
+      (let ((recentf-exclude (list (lambda (_file) t)))
+            (doom-inhibit-large-file-detection t)
+            org-startup-indented
+            org-startup-folded
+            vc-handled-backends
+            org-mode-hook
+            enable-local-variables
+            find-file-hook)
+        (let ((buf (funcall fn file)))
+          (when buf
+            (with-current-buffer buf
+              (add-hook 'doom-switch-buffer-hook #'+org--restart-mode-h
+                        nil 'local)))
+          buf))))
 
   (defadvice! +org--fix-inconsistent-uuidgen-case-a (uuid)
     "Ensure uuidgen is always lowercase (consistent) regardless of system.