Fix returning EGL_BAD_ATTRIBUTE on unknown EGL config attributes.

Bug 23017372

Change-Id: Ie29ca3f67c79b0cb707dda216c256723d3721f28
Reviewed-on: https://swiftshader-review.googlesource.com/3861
Reviewed-by: Ping-Hao Wu <pinghao@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>