[PATCH] org-agenda: fix `org-agenda-new-marker`

In some cases, `org-agenda-buffer` is killed while the symbol itself is still non-nil. `org-agena-new-marker` and anything that calls it would end in a message of "Selecting deleted buffer". This commit simply added an additional test that (buffer-live-p org-agenda-buffer) should also be tru

[PATCH] fix `org-agenda-new-marker`

In some cases, `org-agenda-buffer` is killed while the symbol itself is still non-nil. `org-agena-new-marker` and anything calls it would ends in a message of "Selecting deleted buffer". This commit simply added an additional test that (buffer-live-p org-agenda-buffer) should also be true.