Implement EGL_EXT_client_extensions
Implement EGL_EXT_client_extensions

In EGLQueryString, it is now valid to query EGL_EXTENSIONS
with a display set to EGL_NO_DISPLAY, so the function
should proceed without returning an error in these cases.

Change-Id: I76ccd4f98f3d4180268b6b85b5b04a19bea59977
Reviewed-on: https://swiftshader-review.googlesource.com/9948
Tested-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>

google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader