Fixed LinearBlock thumbnail crash issue

issue tracker id b/222071096
not to send csd with size 0

Test:
Thumbnail preview OK
MMP playback OK

Bug: 222071096
Change-Id: I09e84a4b4d6b37948268225fc7d1fdced75e05f8
diff --git a/media/libstagefright/MediaCodec.cpp b/media/libstagefright/MediaCodec.cpp
index eea5242..c0c8e5d 100644
--- a/media/libstagefright/MediaCodec.cpp
+++ b/media/libstagefright/MediaCodec.cpp
@@ -5956,9 +5956,9 @@
         }
         if (csd->size() == 0) {
             ALOGW("csd-%zu size is 0", i);
+        } else {
+            mCSD.push_back(csd);
         }
-
-        mCSD.push_back(csd);
         ++i;
     }