testrunner: add testcode for #6781 (TemplateSimplifier::simplifyTemplateInstantiations causes heap corruption on invalid code)

Author: matthiaskrgr

test/testgarbage.cpp

@@ -221,6 +221,7 @@ class TestGarbage : public TestFixture {
         TEST_CASE(garbageCode170);
         TEST_CASE(garbageCode171);
         TEST_CASE(garbageCode172);
+        TEST_CASE(garbageCode173); // #6781
         TEST_CASE(garbageValueFlow);
         TEST_CASE(garbageSymbolDatabase);
         TEST_CASE(garbageAST);
@@ -1454,6 +1455,11 @@ class TestGarbage : public TestFixture {
         ASSERT_THROW(checkCode("p<e T=l[<]<>>,"), InternalError);
     }
 
+    void garbageCode173() {
+        // #6781  heap corruption ;  TemplateSimplifier::simplifyTemplateInstantiations
+        ASSERT_THROW(checkCode(" template < Types > struct S : >( S < ...Types... > S <) > { ( ) { } } ( ) { return S < void > ( ) }"), InternalError);
+    }
+
 };
 
 REGISTER_TEST(TestGarbage)