Fix GH-15087 IntlChar::foldCase()'s $option is not optional

Since that parameter is supposed to be optional (and has been prior to
PHP 8.0.0), we fix the implementation instead of the stub.

Closes GH-15091.

NEWS

@@ -18,6 +18,9 @@ PHP                                                                        NEWS
   . Fixed bug GH-14286 (ffi enum type (when enum has no name) make memory
     leak). (nielsdos, dstogov)
 
+- Intl:
+  . Fixed bug GH-15087 (IntlChar::foldCase()'s $option is not optional). (cmb)
+
 - Opcache:
   . Fixed bug GH-13817 (Segmentation fault for enabled observers after pass 4).
     (Bob)

ext/intl/uchar/tests/gh15087.phpt

@@ -0,0 +1,10 @@
+--TEST--
+GH-15087 (IntlChar::foldCase()'s $option is not optional)
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+var_dump(IntlChar::foldCase('I'));
+?>
+--EXPECT--
+string(1) "i"

ext/intl/uchar/uchar.c

@@ -392,8 +392,9 @@ IC_METHOD(foldCase) {
 	zend_string *string_codepoint;
 	zend_long int_codepoint;
 
-	ZEND_PARSE_PARAMETERS_START(2, 2)
+	ZEND_PARSE_PARAMETERS_START(1, 2)
 		Z_PARAM_STR_OR_LONG(string_codepoint, int_codepoint)
+		Z_PARAM_OPTIONAL
 		Z_PARAM_LONG(options)
 	ZEND_PARSE_PARAMETERS_END();