Fix drainer can't be stopped or crashed while stopping (vesoft-inc#2894)

* fix stop crashed

* fix can't exit

src/drainer/DrainerServer.cpp

@@ -123,9 +123,11 @@ bool DrainerServer::start() {
 }
 
 void DrainerServer::waitUntilStop() {
-  std::unique_lock<std::mutex> lkStop(muStop_);
-  while (drainerSvcStatus_ == STATUS_RUNNING) {
-    cvStop_.wait(lkStop);
+  {
+    std::unique_lock<std::mutex> lkStop(muStop_);
+    while (drainerSvcStatus_ == STATUS_RUNNING) {
+      cvStop_.wait(lkStop);
+    }
   }
 
   this->stop();
@@ -157,14 +159,16 @@ void DrainerServer::stop() {
     metaClient_->stop();
   }
 
-  // File operations are not allowed when exiting
-  std::lock_guard<std::mutex> lrk(env_->recvLogMutex_);
-  std::lock_guard<std::mutex> slk(env_->sendLogMutex_);
-  for (auto& fd : env_->recvLogIdFd_) {
-    close(fd.second);
-  }
-  for (auto& fd : env_->sendLogIdFd_) {
-    close(fd.second);
+  if (env_) {
+    // File operations are not allowed when exiting
+    std::lock_guard<std::mutex> lrk(env_->recvLogMutex_);
+    std::lock_guard<std::mutex> slk(env_->sendLogMutex_);
+    for (auto& fd : env_->recvLogIdFd_) {
+      close(fd.second);
+    }
+    for (auto& fd : env_->sendLogIdFd_) {
+      close(fd.second);
+    }
   }
 }