Crash report: https://crash-stats.mozilla.org/report/index/4ac02f69-00b9-43e1-a32c-c0f3c0211128

Reason: SIGSEGV / SEGV_MAPERR

Top 10 frames of crashing thread:

0 libc.so.6 __strcmp_avx2 
1 libxul.so mozilla::gl::EglDisplay::EglDisplay gfx/gl/GLLibraryEGL.cpp:699
2 libxul.so std::__shared_ptr<mozilla::gl::EglDisplay,  /builds/worker/fetches/sysroot-x86_64-linux-gnu/usr/include/c++/7/bits/shared_ptr_base.h:1327
3 libxul.so mozilla::gl::EglDisplay::Create gfx/gl/GLLibraryEGL.cpp:665
4 libxul.so mozilla::gl::GLLibraryEGL::CreateDisplay gfx/gl/GLLibraryEGL.cpp:791
5 libxul.so mozilla::gl::GLContextEGLFactory::CreateImpl gfx/gl/GLContextProviderEGL.cpp:245
6 libxul.so mozilla::gl::GLContextEGLFactory::Create gfx/gl/GLContextProviderEGL.cpp:334
7 libxul.so mozilla::wr::RenderThread::CreateSingletonGL gfx/webrender_bindings/RenderThread.cpp:957
8 libxul.so mozilla::wr::RenderThread::InitDeviceTask gfx/webrender_bindings/RenderThread.cpp:813
9 libxul.so mozilla::detail::runnable_args_base< dom/media/webrtc/transport/runnable_utils.h:41

The result obtained via mLib->fQueryString(mDisplay, LOCAL_EGL_VENDOR) is being tested against a string literal without checking if it's NULL first and apparently it is in this crash. IIRC eglQueryString() can return NULL so that may be why we're crashing there.

A nullptr here probably indicates a buggy driver - we should
handle the case non the less.

https://hg.mozilla.org/mozilla-central/rev/64da1a6eb723