camera: clear ZSLQueue when switching modes

not clearing the queue here will eat up unnecessary memory every time
we switch from video to still mode.

Change-Id: I279ec709b485ca0dab672464e5b829be849bcaa5
diff --git a/services/camera/libcameraservice/api1/Camera2Client.cpp b/services/camera/libcameraservice/api1/Camera2Client.cpp
index 9721e13..8075515 100644
--- a/services/camera/libcameraservice/api1/Camera2Client.cpp
+++ b/services/camera/libcameraservice/api1/Camera2Client.cpp
@@ -825,6 +825,7 @@
         }
         outputStreams.push(getZslStreamId());
     } else {
+        mZslProcessor->clearZslQueue();
         mZslProcessor->deleteStream();
     }