Fix race between SensorManager ctor and callback

Avoids potential invalid memory access if system server crashes during
initialization.

Bug: 132927376
Test: confirm sensors initialize
Change-Id: If7421c452b5893ab2567323d265503a1ce304482

libs/sensor/SensorManager.cpp

diff --git a/libs/sensor/SensorManager.cpp b/libs/sensor/SensorManager.cpp
index 5840d51..96d5eb9 100644
--- a/libs/sensor/SensorManager.cpp
+++ b/libs/sensor/SensorManager.cpp
@@ -94,7 +94,7 @@
 
 SensorManager::SensorManager(const String16& opPackageName)
     : mSensorList(nullptr), mOpPackageName(opPackageName), mDirectConnectionHandle(1) {
-    // okay we're not locked here, but it's not needed during construction
+    Mutex::Autolock _l(mLock);
     assertStateLocked();
 }