So often, in fact, that this bug where it always initialized the memory to 0 survived so long.
Given that the bug went undetected for so long, I think you could almost reasonably claim that calling memset with a nonzero parameter is a "corner case" ;)
It is a "corner case," or close to it, but that's not why it wasn't caught here. I don't think this code is ever called, as explained above. It's default code in case there isn't a platform specific version, but there pretty much always is a platform specific version.
Given that the bug went undetected for so long, I think you could almost reasonably claim that calling memset with a nonzero parameter is a "corner case" ;)