Fix 'return-or-die' statements.

[gugod]

Statements like this:

return do_something() or die "something is wrong";

... are almost certainly mistakes. Since or has lower precedence
than return, it is equivalent to:

( return do_something() ) or die "something_is wrong";

Since return takes the value to caller, the or operator and the
order side of it never executes.

[coveralls]

Coverage decreased (-0.05%) to 90.428% when pulling ffd398a on gugod:master into 0767294 on ukigumo:master.

[coveralls]

Coverage decreased (-0.05%) to 90.428% when pulling ffd398a on gugod:master into 0767294 on ukigumo:master.

[Songmu]

Thanks.