PHP json_encode(): Check depth range before narrowing

[cuishuang]

json_encode() accepts $depth as a zend_long, but stores it directly in the encoder's int max_depth field.

On 64-bit builds, values outside the range of int were silently narrowed before encoding. This could produce platform-dependent behavior.

Check the value with ZEND_LONG_EXCEEDS_INT() before assigning it to encoder.max_depth, and throw a ValueError when it cannot be represented as an int.

Values within the existing range, including depth == 0 and negative values, retain their current behavior.

The regression test covers values above INT_MAX and below INT_MIN.