SurfaceFlinger: prevent division by 0 in Layer::fillInputInfo

Check if scale is 0 before trying to apply it on the window scale.

Bug: 137560795
Bug: 139945549
Test: Set Window Scale Animation to off from developer options menu
Change-Id: Id372d75de5787f62a9cce7c22699216e135bd0f6
Merged-in: I7ae84e2838b1562ff62cdd94484bedba954e1f33
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>