Fix bounds computation of all 0-input filters.

Fix bounds computation of all 0-input filters.

The SkRectShaderImageFilter had the same bug as previously fixed for
SkBitmapSource and SkPictureImageFilter. Rather than copy-and-paste
the implementation, this change makes all filters with 0 inputs return
their source bounds, instead of returning false.

BUG=427251

Review URL: https://codereview.chromium.org/681643003