Crash in webrender::tiling::add_to_batch

[staktrace]

GH issue for https://bugzilla.mozilla.org/show_bug.cgi?id=1424654

> 7 	libxul.so 	core::panicking::panic_bounds_check 	src/libcore/panicking.rs:58
> 8 	libxul.so 	webrender::tiling::add_to_batch 	src/liballoc/vec.rs:0
> 9 	libxul.so 	webrender::picture::PicturePrimitive::add_to_batch 	gfx/webrender/src/tiling.rs:72
> 10 	libxul.so 	webrender::tiling::add_to_batch 	gfx/webrender/src/tiling.rs:886
> 11 	libxul.so 	webrender::picture::PicturePrimitive::add_to_batch 	gfx/webrender/src/tiling.rs:72
> 12 	libxul.so 	webrender::tiling::add_to_batch 	gfx/webrender/src/tiling.rs:886
> 13 	libxul.so 	webrender::picture::PicturePrimitive::add_to_batch 	gfx/webrender/src/tiling.rs:72
> 14 	libxul.so 	webrender::tiling::add_to_batch 	gfx/webrender/src/tiling.rs:886
> 15 	libxul.so 	webrender::picture::PicturePrimitive::add_to_batch 	gfx/webrender/src/tiling.rs:72
> 16 	libxul.so 	webrender::tiling::add_to_batch 	gfx/webrender/src/tiling.rs:886
> 17 	libxul.so 	webrender::picture::PicturePrimitive::add_to_batch 	gfx/webrender/src/tiling.rs:72
> 18 	libxul.so 	webrender::tiling::{{impl}}::build 	gfx/webrender/src/tiling.rs:1118
> 19 	libxul.so 	webrender::render_backend::Document::render 	gfx/webrender/src/tiling.rs:1865
> 20 	libxul.so 	webrender::render_backend::RenderBackend::process_document 	gfx/webrender/src/render_backend.rs:419
> 21 	libxul.so 	webrender::render_backend::RenderBackend::run 	gfx/webrender/src/render_backend.rs:491
> 22 	libxul.so 	std::sys_common::backtrace::__rust_begin_short_backtrace<closure, ()> 	gfx/webrender

[mrobinson]

I have a suspicion that this was fixed by #2249, but due to the line numbers changing I'm not totally certain.

[staktrace]

Per https://bugzilla.mozilla.org/show_bug.cgi?id=1424654#c2 we haven't seen this crash since #2249 merged to gecko, so let's close this.