glsl: Fix buffer overflow with an atomic buffer binding out of range.

glsl: Fix buffer overflow with an atomic buffer binding out of range.

The binding is checked against the limits later in the function, so we
need to make sure we don't overflow before the check here.

Fixes this valgrind warning (and sometimes segfault):

==1460== Invalid write of size 4
==1460==    at 0x74C98DD: ast_declarator_list::hir(exec_list*, _mesa_glsl_parse_state*) (ast_to_hir.cpp:4943)
==1460==    by 0x74C054F: _mesa_ast_to_hir(exec_list*, _mesa_glsl_parse_state*) (ast_to_hir.cpp:159)
==1460==    by 0x7435C12: _mesa_glsl_compile_shader (glsl_parser_extras.cpp:2130)

in

dEQP-GLES31.functional.debug.negative_coverage.get_error.compute.
   exceed_atomic_counters_limit

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>