libbinder_ndk: fix failure when dump/shell are unset

People directly using libbinder_ndk functions who didn't create a debug
dump function function would fail to initialize that pointer, and
potentially crash. Those who didn't create a shell function were
guaranteed to crash. This wasn't noticed because the C++ wrappers which
are the recommended way to use libbinder_ndk always set these functions.

Bug: 161812320
Test: unit tests

Change-Id: I1f6909531bc640097f3f48c4a558fd03f2fa62cb
diff --git a/libs/binder/ndk/tests/iface.cpp b/libs/binder/ndk/tests/iface.cpp
index 64832f3..a588985 100644
--- a/libs/binder/ndk/tests/iface.cpp
+++ b/libs/binder/ndk/tests/iface.cpp
@@ -118,7 +118,7 @@
     AIBinder_Weak_delete(mWeakBinder);
 }
 
-binder_status_t IFoo::addService(const char* instance) {
+AIBinder* IFoo::getBinder() {
     AIBinder* binder = nullptr;
 
     if (mWeakBinder != nullptr) {
@@ -132,8 +132,18 @@
             AIBinder_Weak_delete(mWeakBinder);
         }
         mWeakBinder = AIBinder_Weak_new(binder);
+
+        // WARNING: it is important that this class does not implement debug or
+        // shell functions because it does not use special C++ wrapper
+        // functions, and so this is how we test those functions.
     }
 
+    return binder;
+}
+
+binder_status_t IFoo::addService(const char* instance) {
+    AIBinder* binder = getBinder();
+
     binder_status_t status = AServiceManager_addService(binder, instance);
     // Strong references we care about kept by remote process
     AIBinder_decStrong(binder);