[perl #114576] Optimise if(%hash) in non-void context

[perl #114576] Optimise if(%hash) in non-void context

The boolkeys optimisation (867fa1e2da1) was only applying to an and
(or if) in void context.  If an if occurs as the last thing in a sub-
routine, the void context is not know at compile time so the optimisa-
tion does not apply.

In the case of || (to which the boolkeys optimisation also applies),
we can’t optimise it in non-void context, because someone might be
writing $bucket_info = %hash || '0/0';

In the case of &&, we can optimise it, even in non-void context,
because a true value will always be discarded in %hash && foo.
The false value it returns for an empty hash is always the int-
eger 0.  That would change if we simply applied boolkeys to
my $ret = %hash && foo; because boolkeys return &PL_sv_no (the dualvar
you get from !1).  But since boolkeys’ return value is never directly
visible to perl code, we can safely change that.