Binder: Update to new ScopedLocalRef

Follow-up to commit 625e0007ac07c5aefb4b3d486575ab916116c129 and
commit fac8cb2405999d18aefd75387a5bbdb0c6160e7f.

Bug: 64689630
Test: m
Change-Id: I119cf83a5a54c15973ed3701ee448a9590bb404d
diff --git a/core/jni/android_util_Binder.cpp b/core/jni/android_util_Binder.cpp
index 94e0c5f..af5d12b 100644
--- a/core/jni/android_util_Binder.cpp
+++ b/core/jni/android_util_Binder.cpp
@@ -238,7 +238,7 @@
     env->ExceptionClear();
 
     ScopedLocalRef<jstring> tagstr(env, env->NewStringUTF(LOG_TAG));
-    ScopedLocalRef<jstring> msgstr;
+    ScopedLocalRef<jstring> msgstr(env);
     if (tagstr != nullptr) {
         msgstr.reset(env->NewStringUTF(msg));
     }