glsl: Eliminate out-of-bounds triop_vector_insert

glsl: Eliminate out-of-bounds triop_vector_insert

Section 5.11 (Out-of-Bounds Accesses) of the GLSL 4.60 spec says:

 "In the subsections described above for array, vector, matrix and
  structure accesses, any out-of-bounds access produced undefined
  behavior.... Out-of-bounds writes may be discarded or overwrite
  other variables of the active program."

Fixes crashes when dereferencing gl_ClipDistance and gl_TessLevel*, e.g:

  int index = -1;
  gl_ClipDistance[index] = -1;

When LowerCombinedClipCullDistance is true.

CC: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6363>