Fix crash when redrawing after connecting external monitor

When Kakoune's terminal is shown my laptop monitor and I plug in my
external monitor, the terminal's workspace will move to that external
monitor. When this happens, Kakoune segfaults consistently.

The crash happens in "TerminalUI::Screen::output" where we access a
dangling reference

	    auto output_line = [&](const Line& line) {
	        ColumnCount pending_move = 0;
	        for (auto& [text, skip, face] : line.atoms)
	        {
	/->          if (text.empty() and skip == 0)
	|                continue;
	|
	 cannot access memory referenced by "text"

The stack trace is

	Program received signal SIGSEGV, Segmentation fault.
	0x0000555555a5f1ac in Kakoune::String::Data::is_long (this=0x1a) at /home/johannes/git/kakoune/src/string.hh:180
	(gdb) bt
	#0  0x0000555555a5f1ac in Kakoune::String::Data::is_long (this=0x1a) at /home/johannes/git/kakoune/src/string.hh:180
	mawww#1  0x0000555555a5f1d6 in Kakoune::String::Data::size (this=0x1a) at /home/johannes/git/kakoune/src/string.hh:181
	mawww#2  0x0000555555de34e4 in Kakoune::String::length (this=0x1a) at /home/johannes/git/kakoune/src/string.hh:139
	mawww#3  Kakoune::StringOps<Kakoune::String, char>::empty (this=0x1a) at /home/johannes/git/kakoune/src/string.hh:68
	mawww#4  operator() (__closure=0x7fffffffba50, line=...) at terminal_ui.cc:303
	mawww#5  0x0000555555de45aa in Kakoune::TerminalUI::Screen::output (this=0x5555560a7a60, force=true, synchronized=true, writer=...) at terminal_ui.cc:371
	mawww#6  0x0000555555de548a in Kakoune::TerminalUI::redraw (this=0x5555560a7a40, force=true) at terminal_ui.cc:535
	mawww#7  0x0000555555de579e in Kakoune::TerminalUI::refresh (this=0x5555560a7a40, force=true) at terminal_ui.cc:556
	mawww#8  0x0000555555a9ae71 in Kakoune::Client::redraw_ifn (this=0x55555609f9b0) at client.cc:284
	mawww#9  0x0000555555aab3db in Kakoune::ClientManager::redraw_clients (this=0x7fffffffd060) at client_manager.cc:233
	mawww#10 0x0000555555c86ef8 in Kakoune::run_server (session="", server_init="", client_init="", init_buffer="fish-rust/src/ast.rs", init_coord=..., flags=Kakoune::ServerFlags::None, ui_type=Kakoune::UIType::Terminal,
	    debug_flags=Kakoune::DebugFlags::None, files=ArrayView<Kakoune::StringView> = {...}) at main.cc:908
	mawww#11 0x0000555555c8bb76 in main (argc=2, argv=0x7fffffffe7b8) at main.cc:1263

We check for terminal resize in

	TerminalUI::TerminalUI
	TerminalUI::get_next_key
	TerminalUI::draw
	TerminalUI::suspend

I think neither of those happens when the window is moved.

Looks like TerminalUI::refresh relies on up-to-date dimensions,
so add a resize check here too, fixing the crash.

src/terminal_ui.cc

@@ -550,7 +550,10 @@ void TerminalUI::set_cursor(CursorMode mode, DisplayCoord coord)
 void TerminalUI::refresh(bool force)
 {
     if (m_dirty or force)
+    {
+        check_resize();
         redraw(force);
+    }
     m_dirty = false;
 }