Add param null-check + error return

* Fail gracefully when no hidl is passed

Test: Manually ran with nullptr

Change-Id: I2726c5ad512c7115f4c6e99d1e41e0fe267e6ff2
diff --git a/libs/vr/libvrflinger/vr_flinger.cpp b/libs/vr/libvrflinger/vr_flinger.cpp
index 07f36a4..82ce067 100644
--- a/libs/vr/libvrflinger/vr_flinger.cpp
+++ b/libs/vr/libvrflinger/vr_flinger.cpp
@@ -32,6 +32,9 @@
 VrFlinger::VrFlinger() {}
 
 int VrFlinger::Run(Hwc2::Composer* hidl) {
+  if (!hidl)
+    return EINVAL;
+
   std::shared_ptr<android::pdx::Service> service;
 
   ALOGI("Starting up VrFlinger...");