irc: only use the switch buffer logic during creation

This fixes a problem where calling IRC (e.g. C-c I I) will switch to
a (seemingly random but is ordered by load order) buffer.

It also adds a `user-error` when the IRC workspace is already selected.

modules/app/irc/autoload/irc.el

@@ -7,12 +7,14 @@
              (not inhibit-workspace))
     (+workspace-switch +irc--workspace-name 'auto-create))
   (let ((buffers (doom-buffers-in-mode 'circe-mode nil t)))
+    (if (not (member (window-buffer) buffers))
         (if buffers
             (ignore (switch-to-buffer (car buffers)))
           (require 'circe)
           (delete-other-windows)
           (switch-to-buffer (doom-fallback-buffer))
-      t)))
+          t)
+      (user-error "IRC buffer is already active and selected"))))
 
 ;;;###autoload
 (defun =irc (&optional inhibit-workspace)