Allow null heights to make the screenshot to wrap content

This is very useful when taking screenshots of dynamic height views. We don't always force a view to have a height, and the underlying Facebook implementation allows it by simply not setting a height:

/*
     * Measure and layout the view. In this example we give an exact
     * width but all the height to be WRAP_CONTENT.
     */
    ViewHelpers.setupView(view)
      .setExactWidthDp(300)
      .layout();

Expected behaviour

If I send null as height, I want to take a screenshot with WRAP_CONTENT

Actual behaviour

If I send null as height, I have metrics.heightPixels (fullscreen) as a default

Steps to reproduce

compareScreenshot(
                view = view,
                heightInPx = null,
                widthInPx = 600
            )

Version of the library

4.1+, from the moment shot-android wrapper was released.