AST: Fix crash when printing not yet typechecked associated type decls

Author: slavapestov

lib/AST/ASTDumper.cpp

@@ -642,8 +642,10 @@ namespace {
     void printAbstractTypeParamCommon(AbstractTypeParamDecl *decl,
                                       const char *name) {
       printCommon(decl, name);
-      if (auto superclassTy = decl->getSuperclass()) {
-        OS << " superclass='" << superclassTy->getString() << "'";
+      if (decl->getDeclContext()->getGenericEnvironmentOfContext()) {
+        if (auto superclassTy = decl->getSuperclass()) {
+          OS << " superclass='" << superclassTy->getString() << "'";
+        }
       }
     }