PDFViewer: Fix previous/next page toolbar button icons

go-up.png and go-down.png don't exist (and would look silly here, with
the buttons being next to each other horizontally). Use go-back.png and
go-forward.png instead.

Userland/Applications/PDFViewer/PDFViewerWidget.cpp

@@ -66,13 +66,13 @@ void PDFViewerWidget::create_toolbar()
     toolbar.add_action(*open_outline_action);
     toolbar.add_separator();
 
-    m_go_to_prev_page_action = GUI::Action::create("Go to &Previous Page", Gfx::Bitmap::load_from_file("/res/icons/16x16/go-up.png"), [&](auto&) {
+    m_go_to_prev_page_action = GUI::Action::create("Go to &Previous Page", Gfx::Bitmap::load_from_file("/res/icons/16x16/go-back.png"), [&](auto&) {
         if (m_viewer->current_page() > 0)
             m_page_text_box->set_current_number(m_viewer->current_page());
     });
     m_go_to_prev_page_action->set_enabled(false);
 
-    m_go_to_next_page_action = GUI::Action::create("Go to &Next Page", Gfx::Bitmap::load_from_file("/res/icons/16x16/go-down.png"), [&](auto&) {
+    m_go_to_next_page_action = GUI::Action::create("Go to &Next Page", Gfx::Bitmap::load_from_file("/res/icons/16x16/go-forward.png"), [&](auto&) {
         if (m_viewer->current_page() < m_viewer->document()->get_page_count() - 1)
             m_page_text_box->set_current_number(m_viewer->current_page() + 2);
     });