NPE crash fix.

To reproduce the crash, perform `imageLoader.displayImage()` for a `new ImageView(ctx)` or
```
<?xml version="1.0" encoding="utf-8"?>
<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
```