Lua doesn't have separate integer and floating point numbers,
so we check if a number can fit in an integer and if so convert
it to an integer.
The conversion routine invokes undefined behavior (and even
acknowledges it!). More recent compilers changed their behavior
when casting infinities, breaking test_user_function_double_return
which tests this conversion.
Fix by tightening the conversion to not invoke undefined behavior.
Closesscylladb/scylladb#28503
0add130b9d