SnapdragonCamera: fix a thumbnail update issue

After longshot, mLastJpegData is shown but never cleared. In next shot
if focusing succeeds but no picture taken, the data is shown as thumbnail.

Change-Id: I1f3865bc2db1e600494398d281791f25444dabf8
CRs-Fixed: 890598
diff --git a/src/com/android/camera/PhotoModule.java b/src/com/android/camera/PhotoModule.java
index b7a38dd..f7d7d6b 100644
--- a/src/com/android/camera/PhotoModule.java
+++ b/src/com/android/camera/PhotoModule.java
@@ -2049,6 +2049,7 @@
                mLongshotActive = false;
                mCameraDevice.setLongshot(false);
                mUI.animateCapture(mLastJpegData, mLastJpegOrientation, mMirror);
+               mLastJpegData = null;
                if (!mFocusManager.isZslEnabled()) {
                    setupPreview();
                } else {