PR analyzer/94099 and PR analyzer/94105 both report ICEs relating to
calling region_model::get_lvalue on a NOP_EXPR.

PR analyzer/94099's ICE happens when generating a checker_path when
encountering an unhandled tree code (NOP_EXPR) in get_lvalue with a
NULL context (from for_each_state_change).

PR analyzer/94105 ICE happens when handling an ARRAY_REF where the
first operand is a NOP_EXPR: the unhandled tree code gives us
a symbolic_region, but the case for ARRAY_REF assumes we have an
array_region.

This patch fixes the ICEs by handling NOP_EXPR within
region_model::get_lvalue, and bulletproofs both of the above sources
of failure.

gcc/analyzer/ChangeLog:
	PR analyzer/94099
	PR analyzer/94105
	* diagnostic-manager.cc (for_each_state_change): Bulletproof
	against errors in get_rvalue by passing a
	tentative_region_model_context and rejecting if there's an error.
	* region-model.cc (region_model::get_lvalue_1): When handling
	ARRAY_REF, handle results of error-handling.  Handle NOP_EXPR.

gcc/testsuite/ChangeLog:
	PR analyzer/94099
	PR analyzer/94105
	* gcc.dg/analyzer/pr94099.c: New test.
	* gcc.dg/analyzer/pr94105.c: New test.