Define for Transformations on Path only, also fixed segfault due to GraphicsBuffer

The "invalidated" is used to recycle memory in the GraphicsBuffer,
but that can only be done if there is actually enough memory.

This was causing a segfault if the document was initially empty and had things added to it.
Can now remove the hack in main.cpp where documents started with a {0,0,0,0} RECT in them.

We can now (ab)use the Path for transformations.
The idea was that Arbitrary precision stuff might be faster if we only care about the bounds of the paths.

Unfortunately the way Real was used everywhere will make it a bit difficult to actually use this.
We need Beziers and their bounds to be stored with floats, but the Path bounds to be stored with GMPrat or some other arbitrary type.

It probably won't help that much, but evaluating those Beziers with GMPrat really slows down the CPU renderer.
It's also a giant hack because I still use BezierRenderer for GPU rendering but I now use PathRenderer for CPU rendering of Beziers.

Le sigh.

We can now store Bezier bounds relative to Path bounds and apply transformations only to the Path bounds.