vim-patch:9.1.0046: :drop does not re-use empty buffer (#27165)

Problem:  :drop does not re-use empty buffer
          (Rocco Mao)
Solution: Make :drop re-use an empty buffer
          (Rocco Mao)

fixes: vim/vim#13851
closes: vim/vim#13881

f96dc8d07f

Co-authored-by: Rocco Mao <dapeng.mao@qq.com>

test/functional/ex_cmds/drop_spec.lua

@@ -38,7 +38,7 @@ describe(':drop', function()
                     │^                    |
       {0:~             }│{0:~                   }|*7
       {2:tmp2           }{1:tmp1                }|
-      :drop tmp1                         |
+      "tmp1" [New]                       |
     ]])
   end)