Retain existing range knowledge when prefilling statements.

Retain existing range knowledge when prefilling statements.

When range_of_stmt was adjusted to avoid large recursion depth, we need to
intersect the calculated range whth the any known range to avoid losing
info.  Range_of_stmt does this, but the new prefill code missed it.

	PR tree-optimization/105276
	gcc/
	* gimple-range.cc (gimple_ranger::prefill_stmt_dependencies): Include
	existing global range with calculated value.

	gcc/testsuite/
	* g++.dg/pr105276.C: New.