This is just a minor improvement (optimization) to _setTextData():
Flag shouldAddEllipsis is not changed inside the loop, thus no need
to recalculate the value of additionalWidth for every line of the
original text.
Similar to how it's handled in getWidth() and getHeight() of Konva.Text,
let _setTextData() treat undefined values of the 'width' and 'height'
attributes as if they are set to 'auto', not as if they are fixed.
