vim-patch:9.1.0192: drop: don't rewind when editing the same file

Problem:  :drop tries to :rewind the argumentlist, which results in E37
          (after v9.1.0046)
Solution: instead of calling ex_rewind(), call open_buffer() only when
          re-using the initial empty buffer

fixes: vim/vim#14219
closes: vim/vim#14220

978178823b

Co-authored-by: Christian Brabandt <cb@256bit.org>

src/nvim/ex_cmds2.c

@@ -870,7 +870,9 @@ void ex_drop(exarg_T *eap)
         buf_check_timestamp(curbuf);
         curbuf->b_p_ar = save_ar;
       }
-      ex_rewind(eap);
+      if (buf->b_ml.ml_flags & ML_EMPTY) {
+        open_buffer(false, eap, 0);
+      }
       return;
     }
   }