Untest on unsat bugfix

This commit fixes a bug in Untest when the last sat call was Unsat.
The conflict on untest results in more derivations during backtracking.
This fix ensures that all unit clauses are propagated.
Previously, the unit clause from derivations during untest backtracking
were not propagated.

internal/xo/s.go

@@ -649,7 +649,7 @@ func (s *S) cleanupSolve() {
 		if drvd.TargetLevel < s.endTestLevel {
 			trail.Back(s.endTestLevel)
 			s.x = CNull
-			break
+			//break
 		}
 		trail.Back(drvd.TargetLevel)
 		trail.Assign(drvd.Unit, drvd.P)