Prevent the application to crash when the current page is Date Calculation and users paste a text (#391)

Fix the else condition in ApplicationViewModel::OnPaste

How changes were validated:
Manually

Fixes #389

src/CalcViewModel/ApplicationViewModel.cpp

@@ -189,7 +189,7 @@ void ApplicationViewModel::OnPasteCommand(Object^ parameter)
     {
         ConverterViewModel->OnPasteCommand(parameter);
     }
-    else
+    else if (NavCategory::IsCalculatorViewMode(m_mode))
     {
         CalculatorViewModel->OnPasteCommand(parameter);
     }