The create_dir helper was calling the throwing form of
filesystem::is_directory instead of passing the error_code argument.
Since std::filesystem::create_directory(const path&, error_code&) is
noexcept, it would call std::terminate if an error occurred in
is_directory.

Passing the error_code also takes care of clearing it in the case where
is_directory returns true.

	src/filesystem/ops.cc (create_dir): Pass error_code to is_directory.
	src/filesystem/std-ops.cc (create_dir): Likewise.

From-SVN: r258375