Don't assert on a negative shift.

Don't assert on a negative shift.

Don't assert, simply Return false for negative shifts as we can't tell
anything about the operand.

	PR tree-optimization/97462
	gcc/
	* range-op.cc (operator_lshift::op1_range): Don't trap on negative
	shifts.
	gcc/testsuite/
	* gcc.dg/pr97462.c: New file.