Return ILLEGAL_ARGUMENT for setting null callback

Bug: 299182872
Test: Run VTS with external USB camera
vts-tradefed
> run vts -m VtsAidlHalCameraProvider_TargetTest -t \
    PerInstance/CameraAidlTest#setCallback/0_android_hardware_camera_provider_ICameraProvider_external_0 \
    --logcat-on-failure --logcat-on-failure-size 8192000 \
    --bugreport-on-failure --screenshot-on-failure

Change-Id: I013e3770ddbdcf6475e0927449af6183dcc37a8e
diff --git a/camera/provider/default/ExternalCameraProvider.cpp b/camera/provider/default/ExternalCameraProvider.cpp
index 4d2c847..54875ab 100644
--- a/camera/provider/default/ExternalCameraProvider.cpp
+++ b/camera/provider/default/ExternalCameraProvider.cpp
@@ -75,15 +75,15 @@
 
 ndk::ScopedAStatus ExternalCameraProvider::setCallback(
         const std::shared_ptr<ICameraProviderCallback>& in_callback) {
+    if (in_callback == nullptr) {
+        return fromStatus(Status::ILLEGAL_ARGUMENT);
+    }
+
     {
         Mutex::Autolock _l(mLock);
         mCallback = in_callback;
     }
 
-    if (mCallback == nullptr) {
-        return fromStatus(Status::OK);
-    }
-
     for (const auto& pair : mCameraStatusMap) {
         mCallback->cameraDeviceStatusChange(pair.first, pair.second);
     }