LibGUI: Reduce amount we init for FileIconProvider::filetype_image_icon

Instead of loading every icon, only load the filetype image icon if it
hasn't been already. This icon is used by IconViews that need to lazily
load thumbnails, which don't need any of the other icon types.

Spending the time to load the unneeded images was causing delays to
first paint in BackgroundSettings.

Userland/Libraries/LibGUI/FileIconProvider.cpp

@@ -48,6 +48,15 @@ static void initialize_executable_icon_if_needed()
     s_executable_icon = Icon::default_icon("filetype-executable");
 }
 
+static void initialize_filetype_image_icon_if_needed()
+{
+    static bool initialized = false;
+    if (initialized)
+        return;
+    initialized = true;
+    s_filetype_image_icon = Icon::default_icon("filetype-image");
+}
+
 static void initialize_if_needed()
 {
     static bool s_initialized = false;
@@ -70,8 +79,7 @@ static void initialize_if_needed()
     s_symlink_icon = Icon::default_icon("filetype-symlink");
     s_socket_icon = Icon::default_icon("filetype-socket");
 
-    s_filetype_image_icon = Icon::default_icon("filetype-image");
-
+    initialize_filetype_image_icon_if_needed();
     initialize_executable_icon_if_needed();
 
     for (auto& filetype : config->keys("Icons")) {
@@ -114,7 +122,7 @@ Icon FileIconProvider::home_directory_open_icon()
 
 Icon FileIconProvider::filetype_image_icon()
 {
-    initialize_if_needed();
+    initialize_filetype_image_icon_if_needed();
     return s_filetype_image_icon;
 }