media.log: dump all readers with dumpsys option "r"

Bug: 37153050
Test: builds OK, "dumpsys media.log r" shows all readers
Change-Id: I584dbbeb0532b019441f7aeb4793a9f4e3f6bdda
diff --git a/services/medialog/MediaLogService.h b/services/medialog/MediaLogService.h
index 06c721f..e9211b4 100644
--- a/services/medialog/MediaLogService.h
+++ b/services/medialog/MediaLogService.h
@@ -55,7 +55,7 @@
 
     Mutex               mLock;
 
-    Vector<NBLog::NamedReader> mNamedReaders;
+    Vector<NBLog::NamedReader> mNamedReaders;   // protected by mLock
     NBLog::Shared *mMergerShared;
     NBLog::Merger mMerger;
     NBLog::MergeReader mMergeReader;