libgui: Prevent segfaulting in abandoned ConsumerBase

mConsumer will be null if the ConsumerBase has been abandoned. Prevent
it from being dereferenced in those cases.

Bug 27718219

Change-Id: I9a3ecadb0655ec61cd2fd15ee98b3e1bef078cff
diff --git a/libs/gui/BufferItemConsumer.cpp b/libs/gui/BufferItemConsumer.cpp
index 6f4c89d..3491043 100644
--- a/libs/gui/BufferItemConsumer.cpp
+++ b/libs/gui/BufferItemConsumer.cpp
@@ -49,6 +49,10 @@
 
 void BufferItemConsumer::setName(const String8& name) {
     Mutex::Autolock _l(mMutex);
+    if (mAbandoned) {
+        BI_LOGE("setName: BufferItemConsumer is abandoned!");
+        return;
+    }
     mName = name;
     mConsumer->setConsumerName(name);
 }