CplusPlus: Fix minimal name construction

... when creating the constructor implementation for a derived class.
We would erroneously strip off the class name.
Amends aae3ce15aa.

Change-Id: I62c800d490626e8cb9416829633f9ef7b0c666cd
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cppeditor/cppquickfix_test.cpp

@@ -4404,6 +4404,32 @@ void @func(const N1::S &s);
 void func(const N1::S &s)
 {
 
+}
+)";
+    testDocuments << QuickFixTestDocument::create("file.cpp", original, expected);
+    QuickFixOperationTest(testDocuments, &factory);
+
+    // No using declarations here, but the code model has one. No idea why.
+    testDocuments.clear();
+    original = R"(
+class B {};
+class D : public B {
+    @D();
+};
+)";
+    expected = original;
+    testDocuments << QuickFixTestDocument::create("file.h", original, expected);
+
+    // Source File
+    original = R"(
+#include "file.h"
+)";
+    expected = R"(
+#include "file.h"
+
+D::D()
+{
+
 }
 )";
     testDocuments << QuickFixTestDocument::create("file.cpp", original, expected);