CenterCrop upscales by default

**Glide Version**:Glide 4.6.1

**Integration libraries**:Glide 4.6.1

**Issue details / Repro steps / Use case background**:

**Glide load line / `GlideModule` (if any) / list Adapter code (if any)**:
```java
private String smalImagelUrl= "http://olal87ycc.bkt.clouddn.com/5a4b556e8b171m8ifn4gse4280.jpg!thumb120";
GlideApp.with(this).load(smalImagelUrl).into(imageView);
```

**Layout XML**:
```xml

<>
```

image original size is 120 * 213, and imageview size is 1080 * 1920, and the result bitmap size is 1080 * 1920. the real image size is larger than original size.
i think if original size is small than view size, result bitmap size should used original size.

I know can use override to control bitmap size, but in my cast, the image original size is unknown in advance,

当图片的尺寸小于视图的尺寸的时候，应该使用图片的尺寸，两者取小的那个。