ext/session: session.save_handler - add tests fortwo uncovered cases (#15337)

Author: jorgsowa

ext/session/tests/user_session_module/session_set_save_handler_error5.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Test session_set_save_handler() function : error functionality
+--EXTENSIONS--
+session
+--INI--
+session.save_handler=
+--FILE--
+<?php
+try {
+    session_set_save_handler(new \SessionHandler(), true);
+    session_start();
+} catch (Throwable $e) {
+    echo $e::class . ': ' . $e->getMessage() . "\n";
+}
+echo "ok";
+?>
+--EXPECT--
+Error: Cannot call default session handler
+ok

ext/session/tests/user_session_module/session_set_save_handler_error6.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Test session_set_save_handler() function : error functionality
+--EXTENSIONS--
+session
+--INI--
+session.save_handler=
+--FILE--
+<?php
+ob_start();
+
+session_start();
+session_set_save_handler(new \SessionHandler(), true);
+
+echo "ok";
+ob_end_flush();
+?>
+--EXPECTF--
+Warning: session_start(): Cannot find session save handler "" - session startup failed in %s on line %d
+ok