Fix null pointer exception if partial meta doesn't include some keys

Partial meta may don't have CaptureResult.CONTROL_AE_STATE key set.
In this case, crash happens at onCaptureProgressed(DngCreatorTest.java:734)

Bug: 161734727

Test: android.hardware.camera2.cts.DngCreatorTest#testDngRenderingByBitmapFactor
Change-Id: Ie730b070f4a7a127be9245ef36baf52efc827550
1 file changed