[ASTVerifier] Use hasError() to avoid propagating the error type.

Author: simanerush

lib/AST/ASTVerifier.cpp

@@ -2649,7 +2649,7 @@ class Verifier : public ASTWalker {
         // If we are performing pack iteration, variables have to carry the
         // generic environment. Catching the missing environment here will prevent
         // the code from being lowered.
-        if (var->getTypeInContext()->is<ErrorType>()) {
+        if (var->getTypeInContext()->hasError()) {
           Out << "VarDecl is missing a Generic Environment: ";
           var->getInterfaceType().print(Out);
           Out << "\n";