qbfsat: Fixes three bugs.
qbfsat: Fixes three bugs.

1. Infinite loop in the optimization procedure when the first solution found while maximizing is at zero.
2. A signed-ness issue when maximizing.
3. Erroneously entering bisection mode with no wire to optimize.

YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,SymbiFlow/yosys,antmicro/yosys,SymbiFlow/yosys,antmicro/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,YosysHQ/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys,SymbiFlow/yosys,SymbiFlow/yosys,antmicro/yosys,SymbiFlow/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,antmicro/yosys