json: Improve performance of php_json_encode_array() for non-hooked fields (#20105)

`tmp` can only ever be non-undef if there's a hooked object property, which is
already an `UNEXPECTED()` case. Keep track of whether this case is hit or not
to avoid needlessly calling `zval_ptr_dtor()`.

For:

    <?php

    $len = 0;
    for ($i = 0; $i < 3_000_000; $i++) {
    	$len += strlen(json_encode(array_fill(0, 20, [])));
    }
    var_dump($len);

This is ~1.02 faster for a gcc 13.3 release build on a Intel(R) Core(TM)
i7-1365U.

    Benchmark 1: /tmp/bench/before /tmp/bench/test6.php
      Time (mean ± σ):     762.7 ms ±   3.2 ms    [User: 758.5 ms, System: 2.8 ms]
      Range (min … max):   759.2 ms … 769.3 ms    10 runs

    Benchmark 2: /tmp/bench/after /tmp/bench/test6.php
      Time (mean ± σ):     748.3 ms ±   9.0 ms    [User: 744.3 ms, System: 3.1 ms]
      Range (min … max):   740.8 ms … 766.2 ms    10 runs

    Summary
      /tmp/bench/after /tmp/bench/test6.php ran
        1.02 ± 0.01 times faster than /tmp/bench/before /tmp/bench/test6.php

Author: TimWolla

ext/json/json_encoder.c

@@ -243,6 +243,7 @@ static zend_result php_json_encode_array(smart_str *buf, zval *val, int options,
 		zend_ulong index;
 
 		ZEND_HASH_FOREACH_KEY_VAL_IND(myht, index, key, data) {
+			bool need_dtor = false;
 			zval tmp;
 			ZVAL_UNDEF(&tmp);
 
@@ -264,6 +265,7 @@ static zend_result php_json_encode_array(smart_str *buf, zval *val, int options,
 						if ((prop_info->flags & ZEND_ACC_VIRTUAL) && !prop_info->hooks[ZEND_PROPERTY_HOOK_GET]) {
 							continue;
 						}
+						need_dtor = true;
 						data = zend_read_property_ex(prop_info->ce, Z_OBJ_P(val), prop_info->name, /* silent */ true, &tmp);
 						if (EG(exception)) {
 							PHP_JSON_HASH_UNPROTECT_RECURSION(recursion_rc);
@@ -303,7 +305,9 @@ static zend_result php_json_encode_array(smart_str *buf, zval *val, int options,
 				zval_ptr_dtor(&tmp);
 				return FAILURE;
 			}
-			zval_ptr_dtor(&tmp);
+			if (UNEXPECTED(need_dtor)) {
+				zval_ptr_dtor(&tmp);
+			}
 
 			smart_str_appendc(buf, ',');
 		} ZEND_HASH_FOREACH_END();