NuPlayerSource: clarify getFormat API and fix its usage.

Test: manually run mediaplayer
Bug: 33818804
Change-Id: I1a4e551493fa9521b3b1159182d446e8a9e7d523
diff --git a/media/libmediaplayerservice/nuplayer/StreamingSource.cpp b/media/libmediaplayerservice/nuplayer/StreamingSource.cpp
index 7f9f913..d6b1e8c 100644
--- a/media/libmediaplayerservice/nuplayer/StreamingSource.cpp
+++ b/media/libmediaplayerservice/nuplayer/StreamingSource.cpp
@@ -234,8 +234,7 @@
     }
     status_t err = convertMetaDataToMessage(meta, &format);
     if (err != OK) { // format may have been cleared on error
-        format = new AMessage;
-        format->setInt32("err", err);
+        return NULL;
     }
     return format;
 }