The only possibility with program being nullptr here in the case of GL_LINK_STATUS seems to be if the context gets lost between the validation and usage of `Context::getProgramiv`.

Bug: chromium:991020
Change-Id: I50a77ca4a841dea7324344a71e46d4e0bf72858d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2096176Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shrek Shao <shrekshao@google.com>
Commit-Queue: Shrek Shao <shrekshao@google.com>