VectorDrawable: Use the matrix scale only if the matrix has no rotation or skew.

When canvas is rotated or skewed, the scale factor is affected.
Conservatively reset the scale used to modify path stroke size to 1 in these
cases, since the image will be somewhat blurry anyway with rotation / skew..

b/25418943

Change-Id: I6dff1bca5fac5500fa688c68f8b81b6212526b6b