!3081 修复stream线程未初始化extension_session_vars_array导致的core问题

Merge pull request !3081 from chenxiaobin/fixStreamExtensionVariable

src/common/backend/utils/init/postinit.cpp

@@ -2235,6 +2235,8 @@ void PostgresInitializer::InitStreamSession()
 
     InitSettings();
 
+    InitExtensionVariable();
+
     FinishInit();
 }