imageReader.acquireNextImage failed with ACQUIRE_MAX_IMAGES

It's clear that there are leaked image instances (not closed after use) but I didn't figure out where.

Replacing CamEngine.kt Line 230
```kotlin
var lastImg = imageReader.acquireNextImage()
```
with
```kotlin
var lastImg = imageReader.acquireLatestImage()
```

can be a temporary workaround for the issue, but we'd better find out where the images leaked.