Fix GH-23662: avoid NAN warning in print_r()

[CodedByManish]

Fixes #23662.

print_r() currently converts double values through string coercion, which causes a warning when the value is NAN.

Handle IS_DOUBLE directly in zend_print_zval_r_to_buf() using smart_str_append_double(), so print_r() formats the value without triggering a coercion warning.

Added a regression test covering print_r([NAN]).

Tested with:
./sapi/cli/php -n run-tests.php Zend/tests/gh23662.phpt

Result: PASS.

[ausi]

Should we add the case for print_r(NAN); (without an array) as well?
But I’m not sure if the warning should appear in this case or not.

[CodedByManish]

Should we add the case for print_r(NAN); (without an array) as well? But I’m not sure if the warning should appear in this case or not.

I checked the scalar case as well. print_r(NAN) doesn’t reproduce the warning, while print_r([NAN]) does. So I’ve kept the test focused on the reported case.

[ausi]

print_r(NAN) doesn’t reproduce the warning, while print_r([NAN]) does.

In my test, print_r(NAN) also shows the warning, see https://3v4l.org/LjTUS#veol