dialogs: Show icons in Tips Dialog on Windows

The Previous and Next buttons have arrow icons. However, these
have not shown up on Windows since at least 2.10, as buttons
created with gtk_dialog_add_button () don't automatically make
their icons visible on all platforms.
This patch uses the existing "image" variable to store the icon
rather than passing it inline in gtk_button_set_image ().
This allows us to explicitly set it to be visible so it shows for
all users.

Author: cmyk-student

app/dialogs/tips-dialog.c

@@ -132,15 +132,17 @@ tips_dialog_create (Gimp *gimp)
 
   button = gtk_dialog_add_button (GTK_DIALOG (tips_dialog),
                                   _("_Previous Tip"), RESPONSE_PREVIOUS);
-  gtk_button_set_image (GTK_BUTTON (button),
-                        gtk_image_new_from_icon_name (GIMP_ICON_GO_PREVIOUS,
-                                                      GTK_ICON_SIZE_BUTTON));
+  image = gtk_image_new_from_icon_name (GIMP_ICON_GO_PREVIOUS,
+                                        GTK_ICON_SIZE_BUTTON);
+  gtk_button_set_image (GTK_BUTTON (button), image);
+  gtk_widget_set_visible (image, TRUE);
 
   button = gtk_dialog_add_button (GTK_DIALOG (tips_dialog),
                                   _("_Next Tip"), RESPONSE_NEXT);
-  gtk_button_set_image (GTK_BUTTON (button),
-                        gtk_image_new_from_icon_name (GIMP_ICON_GO_NEXT,
-                                                      GTK_ICON_SIZE_BUTTON));
+  image = gtk_image_new_from_icon_name (GIMP_ICON_GO_NEXT,
+                                        GTK_ICON_SIZE_BUTTON);
+  gtk_button_set_image (GTK_BUTTON (button), image);
+  gtk_widget_set_visible (image, TRUE);
 
   gtk_dialog_set_response_sensitive (GTK_DIALOG (tips_dialog),
                                      RESPONSE_NEXT, tips_count > 1);