clients/nested: fix boolean test

weston_check_egl_extension() returns a bool, not a pointer.

Fixes: ce5b614c80 "clients/nested: use weston_check_egl_extension
                             over strstr"
Cc: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

clients/nested.c

@@ -748,7 +748,7 @@ nested_init_compositor(struct nested *nested)
 
 	nested->egl_display = display_get_egl_display(nested->display);
 	extensions = eglQueryString(nested->egl_display, EGL_EXTENSIONS);
-	if (weston_check_egl_extension(extensions, "EGL_WL_bind_wayland_display") == NULL) {
+	if (!weston_check_egl_extension(extensions, "EGL_WL_bind_wayland_display")) {
 		fprintf(stderr, "no EGL_WL_bind_wayland_display extension\n");
 		return -1;
 	}