Remove dead code trying to handle when the amount of data read is

insufficient to populate the expected struct. Prior to this we already
bailed out of the routine when this situation comes up, so none of this
code had any effect.

If someone wants to bring it back to handle these cases, fixing the
earlier conditions and adding the necessary test cases that actually
exercises it, they can always revert this and go from there.

Both of these were noticed by PVS-Studio due to the identical (dead)
condition.

llvm-svn: 285989