Wayland: Avoid SEGV if a modifier notification comes before the keymap

(cherry picked from commit 0f81598e9f5336a7169f8a6c0c6ce075c7c1c168)
(cherry picked from commit de0cb94e7225539fb283005fc4eebc66a96d3092)

src/video/wayland/SDL_waylandevents.c

@@ -994,6 +994,13 @@ static void keyboard_handle_keymap(void *data, struct wl_keyboard *keyboard,
         return;
     }
 
+    if (input->xkb.keymap != NULL) {
+        /* if there's already a keymap loaded, throw it away rather than leaking it before
+         * parsing the new one
+         */
+        WAYLAND_xkb_keymap_unref(input->xkb.keymap);
+        input->xkb.keymap = NULL;
+    }
     input->xkb.keymap = WAYLAND_xkb_keymap_new_from_string(input->display->xkb_context,
                                                            map_str,
                                                            XKB_KEYMAP_FORMAT_TEXT_V1,
@@ -1016,6 +1023,13 @@ static void keyboard_handle_keymap(void *data, struct wl_keyboard *keyboard,
     input->xkb.idx_caps = 1 << GET_MOD_INDEX(CAPS);
 #undef GET_MOD_INDEX
 
+    if (input->xkb.state != NULL) {
+        /* if there's already a state, throw it away rather than leaking it before
+         * trying to create a new one with the new keymap.
+         */
+        WAYLAND_xkb_state_unref(input->xkb.state);
+        input->xkb.state = NULL;
+    }
     input->xkb.state = WAYLAND_xkb_state_new(input->xkb.keymap);
     if (!input->xkb.state) {
         SDL_SetError("failed to create XKB state\n");
@@ -1061,10 +1075,18 @@ static void keyboard_handle_keymap(void *data, struct wl_keyboard *keyboard,
     }
 
     /* Set up XKB compose table */
+    if (input->xkb.compose_table != NULL) {
+        WAYLAND_xkb_compose_table_unref(input->xkb.compose_table);
+        input->xkb.compose_table = NULL;
+    }
     input->xkb.compose_table = WAYLAND_xkb_compose_table_new_from_locale(input->display->xkb_context,
                                                                          locale, XKB_COMPOSE_COMPILE_NO_FLAGS);
     if (input->xkb.compose_table) {
         /* Set up XKB compose state */
+        if (input->xkb.compose_state != NULL) {
+            WAYLAND_xkb_compose_state_unref(input->xkb.compose_state);
+            input->xkb.compose_state = NULL;
+        }
         input->xkb.compose_state = WAYLAND_xkb_compose_state_new(input->xkb.compose_table,
                                                                  XKB_COMPOSE_STATE_NO_FLAGS);
         if (!input->xkb.compose_state) {
@@ -1299,6 +1321,12 @@ static void keyboard_handle_modifiers(void *data, struct wl_keyboard *keyboard,
     Wayland_Keymap keymap;
     const uint32_t modstate = (mods_depressed | mods_latched | mods_locked);
 
+    if (input->xkb.state == NULL) {
+        /* if we get a modifier notification before the keymap, there's nothing we can do with the information
+        */
+        return;
+    }
+
     WAYLAND_xkb_state_update_mask(input->xkb.state, mods_depressed, mods_latched,
                                   mods_locked, 0, 0, group);