ApplyScissorViewport with disjoint scissor and scissorViewport causes crash in debug, undefined behaviour in release

[Jmangles]

Describe the bug
When ApplyScissorViewport is called with disjoint rects, an assertion fails in debug builds and can cause underflow in release builds.

To Reproduce
In our project we encountered this using FilaGui and ImPlot, dragging the application from one display to another of a different resolution would crash reliably in debug builds due to the assertion.

Expected behavior
The issue is handled gracefully either through error propagation or ensuring the values are valid.