Promote warning to value error in strpbrk()

Closes GH-4598

Author: Girgias

ext/standard/string.c

@@ -6068,8 +6068,8 @@ PHP_FUNCTION(strpbrk)
 	ZEND_PARSE_PARAMETERS_END();
 
 	if (!ZSTR_LEN(char_list)) {
-		php_error_docref(NULL, E_WARNING, "The character list cannot be empty");
-		RETURN_FALSE;
+		zend_value_error("The character list cannot be empty");
+		return;
 	}
 
 	for (haystack_ptr = ZSTR_VAL(haystack); haystack_ptr < (ZSTR_VAL(haystack) + ZSTR_LEN(haystack)); ++haystack_ptr) {

ext/standard/tests/strings/strpbrk_error.phpt

@@ -8,18 +8,16 @@ Test strpbrk() function : error conditions
  * Alias to functions:
  */
 
-echo "*** Testing strpbrk() : error conditions ***\n";
-
 $haystack = 'This is a Simple text.';
 
-echo "\n-- Testing strpbrk() function with empty second argument --\n";
-var_dump( strpbrk($haystack, '') );
+echo "-- Testing strpbrk() function with empty second argument --\n";
+try {
+    strpbrk($haystack, '');
+} catch (\ValueError $e) {
+    echo $e->getMessage() . "\n";
+}
 
 ?>
---EXPECTF--
-*** Testing strpbrk() : error conditions ***
-
+--EXPECT--
 -- Testing strpbrk() function with empty second argument --
-
-Warning: strpbrk(): The character list cannot be empty in %s on line %d
-bool(false)
+The character list cannot be empty