Crash in draw_paint_node

How to reproduce:

1. Start latest Weston (2df71c6d) under X11 (may work with other backends, but I haven't tested)
2. Start pavucontrol (ensuring it runs natively in the just started Weston instance).
3. Go to the "Input devices" tab.
4. Click on the "Port" drop down menu of the device (only one device in my case)
5. Crash (it may take a few clicks at step 4)

The gdb log is:

Thread 1 "weston" received signal SIGSEGV, Segmentation fault.
0x00007ffff72aa718 in draw_paint_node (pnode=0x555555c35610, damage=0x7fffffffcf50) at ../libweston/renderer-gl/gl-renderer.c:1017
1017		if (gb->shader_variant == SHADER_VARIANT_NONE &&
(gdb) bt
#0  0x00007ffff72aa718 in draw_paint_node (pnode=0x555555c35610, damage=0x7fffffffcf50) at ../libweston/renderer-gl/gl-renderer.c:1017
#1  0x00007ffff72aabf1 in repaint_views (output=0x555555c14f60, damage=0x7fffffffcf50) at ../libweston/renderer-gl/gl-renderer.c:1108
#2  0x00007ffff72ac6b8 in gl_renderer_repaint_output (output=0x555555c14f60, output_damage=0x7fffffffd020) at ../libweston/renderer-gl/gl-renderer.c:1702
#3  0x00007ffff7f9c73a in x11_output_repaint_gl (output_base=0x555555c14f60, damage=0x7fffffffd020) at ../libweston/backend-x11/x11.c:425
#4  0x00007ffff7d58e51 in weston_output_repaint (output=0x555555c14f60) at ../libweston/compositor.c:3117
#5  0x00007ffff7d59110 in weston_output_maybe_repaint (output=0x555555c14f60, now=0x7fffffffd100) at ../libweston/compositor.c:3183
#6  0x00007ffff7d592e8 in output_repaint_timer_handler (data=0x55555556b380) at ../libweston/compositor.c:3250
#7  0x00007ffff7d208e2 in wl_timer_heap_dispatch (timers=0x555555562fa8) at ../src/event-loop.c:526
#8  wl_event_loop_dispatch (loop=0x555555562f60, timeout=timeout@entry=-1) at ../src/event-loop.c:1020
#9  0x00007ffff7d1e2b5 in wl_display_run (display=0x555555568e40) at ../src/wayland-server.c:1408
#10 0x00007ffff7fb5f24 in wet_main (argc=1, argv=0x7fffffffd948, test_data=0x0) at ../compositor/main.c:3589
#11 0x000055555555515e in main (argc=6, argv=0x7fffffffd948) at ../compositor/executable.c:33
(gdb) info locals 
gr = 0x55555558b270
gs = 0x555555c35730
gb = 0x0
buffer = 0x0
repaint = {extents = {x1 = 0, y1 = 32, x2 = 1596, y2 = 1757}, data = 0x0}
surface_opaque = {extents = {x1 = 26, y1 = 23, x2 = 3222, y2 = 1817}, data = 0x555555c6d070}
surface_blend = {extents = {x1 = 0, y1 = 0, x2 = 3248, y2 = 1846}, data = 0x555555c0bf20}
filter = 9728
sconf = {req = {variant = 2, input_is_premult = true, green_tint = false, color_pre_curve = 0, color_mapping = 0, pad_bits_ = 0}, projection = {d = {0.00125313282, 0, 0, 0, 0, -0.00113830389, 0, 0, 0, 0, 1, 0, 
      -1, 1, 0, 1}, type = 3}, view_alpha = 1, unicolor = {0, 0, 0, 0}, input_tex_filter = 9728, input_tex = {5, 0, 0}, color_pre_curve_lut_tex = 0, color_pre_curve_lut_scale_offset = {0, 0}, color_mapping = {
    lut3d = {tex = 0, scale_offset = {0, 0}}}}