Sema: Check worseThanBestSolution() in a better place

Author: slavapestov

lib/Sema/CSStep.cpp

@@ -924,6 +924,7 @@ StepResult ConjunctionStep::resume(bool prevFailed) {
 
   // Rewind back the constraint system information.
   ActiveChoice.reset();
+  restoreBestScore();
 
   if (CS.isDebugMode())
     getDebugLogger() << ")\n";

lib/Sema/CSStep.h

@@ -530,6 +530,9 @@ template <typename P> class BindingStep : public SolverStep {
     if (CS.isTooComplex(Solutions))
       return done(/*isSuccess=*/false);
 
+    if (CS.worseThanBestSolution())
+      return done(/*isSuccess=*/false);
+
     while (auto choice = Producer()) {
       if (shouldSkip(*choice))
         continue;