fix EncapsulateFieldTests

Factory_NullSelectionReturnsNullPresenter relied on the implementation
for GetQualifiedSelection() of the actual code. Mocks didn't follow suit
and returned non-null QualifiedSelection for empty Selection instances.

For whatever reason we can't set the mock up to CallBase() so we need to
special case it. Using a ternary inside the lambda results in a compiler
error

Author: Vogel612

RubberduckTests/Mocks/MockProjectBuilder.cs

@@ -332,8 +332,10 @@ private Mock<ICodePane> CreateCodePaneMock(string name, Selection selection, Moc
             var window = windows.CreateWindow(name);
             windows.Add(window);
 
-            codePane.Setup(p => p.GetQualifiedSelection()).Returns(() =>
-                new QualifiedSelection(new QualifiedModuleName(component.Object), selection));
+            codePane.Setup(p => p.GetQualifiedSelection()).Returns(() => {
+                if (selection.IsEmpty()) { return null; }
+                return new QualifiedSelection(new QualifiedModuleName(component.Object), selection);
+            });
             codePane.SetupProperty(p => p.Selection, selection);
             codePane.Setup(p => p.Show());