sdl2: Diplomacy dialogs removed while iterating them
sdl2-client popdown_diplomacy_dialogs() calls popdown_diplomacy_dialog() inside dialog_list_iterate(). That call frees the dialog, causing next iteration to use already-freed link.
Also a version to push to S2_6
sdl2-client popdown_diplomacy_dialogs() calls popdown_diplomacy_dialog() inside dialog_list_iterate(). That call frees the dialog, causing next iteration to use already-freed link.