Doing the test at exit of the function avoids an unnecessary
test and branch inside longjmp().

Semantics are unchanged.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>