[CSApply] Make sure that hole type are not propagated to AST

Author: xedin

lib/Sema/CSApply.cpp

@@ -7662,6 +7662,8 @@ namespace {
       //       "Mismatched types!");
       assert(!exprType->hasTypeVariable() &&
              "Should not write type variable into expression!");
+      assert(!exprType->hasHole() &&
+             "Should not write type holes into expression!");
       expr->setType(exprType);
 
       if (auto kp = dyn_cast<KeyPathExpr>(expr)) {