taskbar: Wait for terminated child windows

apps/taskbar.cpp

@@ -1,15 +1,24 @@
 #include <os/Process.h>
+#include <signal.h>
+#include <sys/wait.h>
 #include <ui/App.h>
 #include <ui/Button.h>
 #include <ui/Container.h>
 #include <ui/Image.h>
 #include <ui/Layout.h>
 
+void sigchld_handler(int)
+{
+    wait(nullptr);
+}
+
 Result<int> luna_main(int argc, char** argv)
 {
     ui::App app;
     TRY(app.init(argc, argv));
 
+    signal(SIGCHLD, sigchld_handler);
+
     ui::Rect screen = app.screen_rect();
 
     ui::Rect bar = ui::Rect { ui::Point { 0, screen.height - 50 }, screen.width, 50 };