fix(terminal): possible missing refresh with buffer updates (#38388)

Problem:
Terminal refresh may be missed if buffer update callbacks poll for uv
events. Example test failure on FreeBSD:

FAILED   test/functional/terminal/buffer_spec.lua @ 1049: :terminal buffer scrollback is correct if buffer update callbacks poll for uv events
test/functional/terminal/buffer_spec.lua:1004: Row 1 did not match.
Expected:
  |*19995: TEST{MATCH: +}|
  |*19996: TEST{MATCH: +}|
  |*19997: TEST{MATCH: +}|
  |*19998: TEST{MATCH: +}|
  |*19999: TEST{MATCH: +}|
  |^[Process exited 0]                                |
  |{5:-- TERMINAL --}                                    |
Actual:
  |*19696: TEST                                       |
  |*19697: TEST                                       |
  |*19698: TEST                                       |
  |*19699: TEST                                       |
  |*19700: TEST                                       |
  |^[Process exited 0]                                |
  |{5:-- TERMINAL --}                                    |

Solution:
Call changed_lines() after resetting invalid region in refresh_screen().
Handle terminal being invalidated in the middle of refresh_timer_cb().

0 files changed, 0 insertions, 0 deletions