Do not set camera preview display if the surface is null.

MediaRecorder.setPreviewDisplay() is not required if applications
use MediaRecorder.setCamera(). Besides, this causes a problem when
apps use Camera.setPreviewTexture. Camera service thinks the
surface texture from Camera.setPreviewTexture and the surface from
MediaRecorder.setPreviewDisplay are different.

bug:5988937

Change-Id: Ia345705b6679ef349db6e354feaa3cc0fe8bcd8c
diff --git a/media/libstagefright/CameraSource.cpp b/media/libstagefright/CameraSource.cpp
index 2df5528..3ddad93 100755
--- a/media/libstagefright/CameraSource.cpp
+++ b/media/libstagefright/CameraSource.cpp
@@ -515,9 +515,13 @@
         return err;
     }
 
-    // This CHECK is good, since we just passed the lock/unlock
-    // check earlier by calling mCamera->setParameters().
-    CHECK_EQ((status_t)OK, mCamera->setPreviewDisplay(mSurface));
+    // Set the preview display. Skip this if mSurface is null because
+    // applications may already set a surface to the camera.
+    if (mSurface != NULL) {
+        // This CHECK is good, since we just passed the lock/unlock
+        // check earlier by calling mCamera->setParameters().
+        CHECK_EQ((status_t)OK, mCamera->setPreviewDisplay(mSurface));
+    }
 
     // By default, do not store metadata in video buffers
     mIsMetaDataStoredInVideoBuffers = false;