Fix bool return types

This makes wlroots build in C23 mode.

C23 is more strict and rejects implicit conversions from bool to a
pointer.

backend/x11/backend.c

@@ -600,7 +600,7 @@ struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
 
 	if (!query_formats(x11)) {
 		wlr_log(WLR_ERROR, "Failed to query supported DRM formats");
-		return false;
+		goto error_event;
 	}
 
 	x11->drm_fd = -1;
@@ -637,7 +637,7 @@ struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
 #if HAVE_XCB_ERRORS
 	if (xcb_errors_context_new(x11->xcb, &x11->errors_context) != 0) {
 		wlr_log(WLR_ERROR, "Failed to create error context");
-		return false;
+		goto error_event;
 	}
 #endif
 

render/vulkan/renderer.c

@@ -1816,12 +1816,12 @@ struct wlr_vk_pipeline_layout *get_or_create_pipeline_layout(
 	if (res != VK_SUCCESS) {
 		wlr_vk_error("vkCreateSampler", res);
 		free(pipeline_layout);
-		return false;
+		return NULL;
 	}
 
 	if (!init_tex_layouts(renderer, pipeline_layout->sampler, &pipeline_layout->ds, &pipeline_layout->vk)) {
 		free(pipeline_layout);
-		return false;
+		return NULL;
 	}
 
 	wl_list_insert(&renderer->pipeline_layouts, &pipeline_layout->link);

render/vulkan/texture.c

@@ -806,7 +806,7 @@ static struct wlr_texture *vulkan_texture_from_dmabuf_buffer(
 
 	struct wlr_vk_texture *texture = vulkan_texture_from_dmabuf(renderer, dmabuf);
 	if (texture == NULL) {
-		return false;
+		return NULL;
 	}
 
 	texture->buffer = wlr_buffer_lock(buffer);

types/output/render.c

@@ -52,12 +52,12 @@ static struct wlr_buffer *output_acquire_empty_buffer(struct wlr_output *output,
 	// wlr_output_test_state(), which will prevent us from being called.
 	if (!wlr_output_configure_primary_swapchain(output, state,
 			&output->swapchain)) {
-		return false;
+		return NULL;
 	}
 
 	struct wlr_buffer *buffer = wlr_swapchain_acquire(output->swapchain, NULL);
 	if (buffer == NULL) {
-		return false;
+		return NULL;
 	}
 
 	struct wlr_render_pass *pass =