Move non-word-aligned thus-padded field down after aligned fields
based on profile data.  (I don't feel this should matter, but
it shouldn't hurt so this change at least gets it out of the way
while we work on more profiles and more important performance
updates.)
Don't check for NULL key names during hash lookup for the interned string case.
Since no strcmp is happening, it wouldn't cause a crash even if there were a
bug that caused a NULL there, and keys are not allowed to be NULL so it should
never happen.  Furthermore, we never guarded the passed-in name from being NULL,
which would be required to have the pointer equals be true when comparing to
a NULL key.