camera2: Fix segfault when using null availability listener

ICameraService::addListener / removeListener will now return BAD_VALUE
if a null listener is used.

Bug: 12891434
Change-Id: I9764110094d8fd42e22fcc8df3ef0e73c1b070e7
diff --git a/services/camera/libcameraservice/CameraService.cpp b/services/camera/libcameraservice/CameraService.cpp
index eeedfc9..5957d97 100644
--- a/services/camera/libcameraservice/CameraService.cpp
+++ b/services/camera/libcameraservice/CameraService.cpp
@@ -655,6 +655,11 @@
                                 const sp<ICameraServiceListener>& listener) {
     ALOGV("%s: Add listener %p", __FUNCTION__, listener.get());
 
+    if (listener == 0) {
+        ALOGE("%s: Listener must not be null", __FUNCTION__);
+        return BAD_VALUE;
+    }
+
     Mutex::Autolock lock(mServiceLock);
 
     Vector<sp<ICameraServiceListener> >::iterator it, end;
@@ -683,6 +688,11 @@
                                 const sp<ICameraServiceListener>& listener) {
     ALOGV("%s: Remove listener %p", __FUNCTION__, listener.get());
 
+    if (listener == 0) {
+        ALOGE("%s: Listener must not be null", __FUNCTION__);
+        return BAD_VALUE;
+    }
+
     Mutex::Autolock lock(mServiceLock);
 
     Vector<sp<ICameraServiceListener> >::iterator it;