generator::is_isl_ctx: avoid implicit conversion to bool
generator::is_isl_ctx: avoid implicit conversion to bool

The implicit conversion dates back to isl-0.07-222-g115763537
(add extract_interface for constructing interfaces to other languages,
Tue Aug 2 12:58:48 2011 +0200).

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl