Fix Bug #79448 0 is a valid Unicode codepoint, but mb_substitute_character(0) fails

Author: Girgias

ext/mbstring/mbstring.c

@@ -2038,7 +2038,7 @@ PHP_FUNCTION(mb_detect_order)
 
 static inline int php_mb_check_code_point(zend_long cp)
 {
-	if (cp <= 0 || cp >= 0x110000) {
+	if (cp < 0 || cp >= 0x110000) {
 		/* Out of Unicode range */
 		return 0;
 	}

ext/mbstring/tests/bug79448.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Bug #79448 	0 is a valid Unicode codepoint, but mb_substitute_character(0) fails
+--SKIPIF--
+<?php extension_loaded('mbstring') or die('skip mbstring not available'); ?>
+--FILE--
+<?php
+// 0 is a valid codepoint regardless of encoding
+var_dump(mb_substitute_character(0));
+?>
+--EXPECT--
+bool(true)