Avoid potential race condition in test setup

Resize the event queue before starting the polling thread to avoid
potential concurrent access.

Test: run VtsHalSensorsV2_0TargetTest
Change-Id: I71af46169e7731df4135639644665365b3714e1f
diff --git a/sensors/2.0/vts/functional/SensorsHidlEnvironmentV2_0.cpp b/sensors/2.0/vts/functional/SensorsHidlEnvironmentV2_0.cpp
index 03fcc17..dc54f27 100644
--- a/sensors/2.0/vts/functional/SensorsHidlEnvironmentV2_0.cpp
+++ b/sensors/2.0/vts/functional/SensorsHidlEnvironmentV2_0.cpp
@@ -130,8 +130,8 @@
 
 void SensorsHidlEnvironmentV2_0::startPollingThread() {
     mStopThread = false;
-    mPollThread = std::thread(pollingThread, this);
     mEvents.reserve(MAX_RECEIVE_BUFFER_EVENT_COUNT);
+    mPollThread = std::thread(pollingThread, this);
 }
 
 void SensorsHidlEnvironmentV2_0::readEvents() {