Add missing return statements to tests.

Change-Id: I2890e67e383f8af88a9175e4497c5167c6d22468

IO/Export/Testing/Cxx/TestGL2PSTextActor3D.cxx

@@ -103,4 +103,6 @@ int TestGL2PSTextActor3D(int, char *[])
   win->SetMultiSamples(0);
   win->GetInteractor()->Initialize();
   win->GetInteractor()->Start();
+
+  return EXIT_SUCCESS;
 }

Rendering/Matplotlib/Testing/Cxx/TestMathTextActor.cxx

@@ -100,4 +100,6 @@ int TestMathTextActor(int, char *[])
   win->SetMultiSamples(0);
   win->GetInteractor()->Initialize();
   win->GetInteractor()->Start();
+
+  return EXIT_SUCCESS;
 }

Rendering/Matplotlib/Testing/Cxx/TestMathTextActor3D.cxx

@@ -103,4 +103,6 @@ int TestMathTextActor3D(int, char *[])
   win->SetMultiSamples(0);
   win->GetInteractor()->Initialize();
   win->GetInteractor()->Start();
+
+  return EXIT_SUCCESS;
 }