egl/x11: Fix swap interval setup

Calling dri2_x11_setup_swap_interval with swap_available = false
sets the min/max/default swap interval values to zero.
EGL_MIN/MAX_SWAP_INTERVAL is always reported as 0 and the interval
value set by eglSwapInterval gets clamped to 0.

Set swap_available to true before calling dri2_x11_setup_swap_interval,
as was done before.

Fixes: c00701c83a ("egl/x11: unify swrast/kopper/dri3 paths a bit")
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34235>

src/egl/drivers/dri2/platform_x11.c

@@ -1780,14 +1780,13 @@ platform_x11_finalize(_EGLDisplay *disp)
    dri2_setup_screen(disp);
 
    if (!dri2_dpy->swrast) {
-      dri2_x11_setup_swap_interval(disp);
-
 #ifdef HAVE_WAYLAND_PLATFORM
       if (dri2_dpy->kopper)
          dri2_dpy->device_name = strdup("zink");
 #endif
 
       dri2_dpy->swap_available = true;
+      dri2_x11_setup_swap_interval(disp);
       if (dri2_dpy->fd_render_gpu == dri2_dpy->fd_display_gpu)
          disp->Extensions.KHR_image_pixmap = EGL_TRUE;
       disp->Extensions.NOK_texture_from_pixmap = EGL_TRUE;