Handle offscreen animations correctly

A bug in software rendering caused animations on views that are offscreen
to not get drawn, therefore the animation doesn't continue (since old-style
animations depend on the logic in the drawing code to keep running). Fix is
to special case the isAnimating case in ViewRoot to go ahead and schedule
a traversal even if the dirty rect does not intersect with the visible region.

Issue #7396035 Animations starting offscreen don't draw run/end/draw properly (sw rendering only)

Change-Id: Iae25b3a424ddc5a16ba431ecd68cf42d5500db3f