Fix issue with xml GradientDrawables consuming both resources

and parameters provided by the Theme leading to array size
mismatch exceptions being thrown.

GradientDrawable#updateGradientDrawableGradient is invoked multiple
times during xml inflation, once with the attributes provided in the xml
and another with attributes provided in the Theme. However, if
parameters come from both the xml resources and the theme, when
theme attributes are applied it can partially squash previously applied
values.

In the case of gradients this can lead to a previously initialized
positions array with floating point offsets for color positions
being applied but not overriden with theme attributes that only include
a portion of the attribute values leading to exceptions being thrown
as the colors and positions arrays are not of the same size

Bug: 112122447
Test: Created test of xml inflation of GradientDrawables both with and
without theme attributes

Change-Id: Ie4183e2304677d30b6faef1cdc5c1be27ef9edd4