transient--post-command: Only clear variables on real post-command

In [1: 0e0ece3] we started clearing `transient-current-*' variables
here instead of in `transient--post-exit', to make sure their values
are nil in timers and while using the minibuffer.

The latter was achieved by clearing even during the premature call to
`transient--post-command', which occurs when the minibuffer is entered,
i.e., when suspending the transient.  Unfortunately transient state
cannot be resumed until the outer command really is done, and as a
result these variables remained cleared for the current command after
any use of the minibuffer.

This obviously can be fixed by only clearing on the real `post-command'
run, but that of course means that these variables are once more
accessible during minibuffer use.  There does not appear to be a way
around that, but luckily it is unlikely that that would actually lead
to any unexpected behavior.

Closes #292.

1: 2024-06-26 0e0ece3
   transient--post-command: Clear transient-current-* variables here

lisp/transient.el

@@ -2553,11 +2553,10 @@ value.  Otherwise return CHILDREN as is."
                  (transient--pop-keymap 'transient--redisplay-map)
                  (setq transient--redisplay-map new)
                  (transient--push-keymap 'transient--redisplay-map))
-               (transient--redisplay))))))
-  (transient--debug 'clear-current)
-  (setq transient-current-prefix nil)
-  (setq transient-current-command nil)
-  (setq transient-current-suffixes nil))
+               (transient--redisplay)))))
+    (setq transient-current-prefix nil)
+    (setq transient-current-command nil)
+    (setq transient-current-suffixes nil)))
 
 (defun transient--post-exit (&optional command)
   (transient--debug 'post-exit)