Init the static member when first used for CursorWindow.

As the CursorWindow will be preloaded by zygote, and there is one static
member need use the system resource to initialize. But actually the zygote
do not preload the resource now. (In fact, the zygote will preload classes
first, then preload the resource.) We need ensure the zygote to create the
system resource first.

So change to init this static member as -1, and it will be evaluated when
first used.

Change-Id: Ibccb84e3c410c73788ac682fe76b720306e81dc4