fix(windows): don't set window icon on SIGHUP #34260

Problem:  When using conhost and pressing the 'x' button
          to close it while nvim is open, nvim hangs up
          while trying to reset the window icon, causing a big
          delay before the terminal actually closes. #34171

Solution: Set the window handle to NULL after receiving SIGHUP
          so that nvim will not try resetting the icon.

src/nvim/os/os_win_console.c

@@ -29,6 +29,11 @@ int os_open_conin_fd(void)
   return conin_fd;
 }
 
+void os_clear_hwnd(void) 
+{
+    hWnd = NULL;
+}
+
 void os_replace_stdin_to_conin(void)
 {
   close(STDIN_FILENO);

src/nvim/os/signal.c

@@ -23,6 +23,10 @@
 # include "nvim/memline.h"
 #endif
 
+#ifdef MSWIN
+# include "nvim/os/os_win_console.h"
+#endif
+
 static SignalWatcher spipe, shup, squit, sterm, susr1, swinch, ststp;
 #ifdef SIGPWR
 static SignalWatcher spwr;
@@ -218,12 +222,15 @@ static void on_signal(SignalWatcher *handle, int signum, void *data)
       autowrite_all();
     }
     break;
+#endif
+  case SIGHUP:
+#ifdef MSWIN
+    os_clear_hwnd();
 #endif
   case SIGTERM:
 #ifdef SIGQUIT
   case SIGQUIT:
 #endif
-  case SIGHUP:
     if (!rejecting_deadly) {
       deadly_signal(signum);
     }