three.js postprocessing dof example has GL error

[jdm]

https://threejs.org/examples/webgl_postprocessing_dof.html

ERROR 2018-06-06T17:08:20Z: canvas::webgl_thread: Last GL operation failed: DrawElements(4, 6, 5123, 0)
assertion failed: `(left == right)`
  left: `1286`,
 right: `0`: Unexpected WebGL error: 0x506 (1286) (thread WebGLThread, at components/canvas/webgl_thread.rs:1030)
ERROR 2018-06-06T17:08:20Z: canvas::canvas_data: Unimplemented canvas2d.fillText. Values received: 51 MS (7-174), 6, 4, None.
stack backtrace:
   0:        0x10286714e - backtrace::backtrace::trace::h0217a35a27c6669c
   1:        0x102867c2c - _$LT$backtrace..capture..Backtrace$u20$as$u20$core..default..Default$GT$::default::he8a822a2cccc31d4
   2:        0x102867c7d - backtrace::capture::Backtrace::new::hc727cc4a6b9e93b8
   3:        0x10012279e - servo::main::_$u7b$$u7b$closure$u7d$$u7d$::h619243cbcb02c412
   4:        0x102876dce - std::panicking::rust_panic_with_hook::h90a47ec287d0101d
   5:        0x102876900 - std::panicking::begin_panic_fmt::h7be80a894b2b7fab
   6:        0x101a63347 - canvas::webgl_thread::WebGLImpl::apply::h13716cfaea649d87
   7:        0x101a5e150 - _$LT$canvas..webgl_thread..WebGLThread$LT$VR$C$$u20$OB$GT$$GT$::handle_webgl_command::h6a534ef73f67943e
   8:        0x101a32220 - std::sys_common::backtrace::__rust_begin_short_backtrace::h990fc7ccc23ba878
   9:        0x101a08334 - std::panicking::try::do_call::h66683ea52a2df1d6 (.llvm.9678968464668631832)
  10:        0x10289932e - __rust_maybe_catch_panic
  11:        0x101a39d72 - _$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$::call_box::he1afdd2e343b2b00
  12:        0x10288a067 - std::sys_common::thread::start_thread::hfa2857da5a919ab1
  13:        0x102870378 - std::sys::unix::thread::Thread::new::thread_start::h8abec15fd1655cac
  14:     0x7fffcec8293a - _pthread_body
  15:     0x7fffcec82886 - _pthread_start

[jdm]

No more GL error!