Fix rendering on Parallels VMs with graphics set to "low"

[mcgroarty]

Description

This allows Second Life to render properly when running in a Parallels virtual machine - Windows on Apple Silicon

Issue 1: Matrices were used uninitialized.

In LLRender::syncMatrices():

• Treat uniform location 0 as valid when uploading the inverse model-view, inverse projection, and identity matrices. Only location -1 indicates that a uniform is absent. (This is a zero-based index.)

Issue 2: Parallels GLSL compilation:

• return float literals (not ints) from functions declared to return float

  • Parallels' shader compiler rejects these in their current form. These will be a NOP with compilers that automatically cast the ints to floats.

• rename the local waterClip() wrapper to avoid an overload conflict

  • I think Parallels is in the wrong by not allowing the local overload, but the workaround creates no overhead on other platforms.

Related Issues

• [ x ] Please link to a relevant GitHub issue for additional context.
  • Bug Fix: Second Life renders mostly-white screens under Parallels

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