[apps/code] Check that app can be exited before switching to DFU

This fixes the following crash: create a script which contains only
"input()". Execute it, then while in the input, plug in the calculator.
When un-plugging it, the device crashes.

apps/code/app.cpp

@@ -88,6 +88,7 @@ App::App(Container * container, Snapshot * snapshot) :
 }
 
 App::~App() {
+  assert(!m_consoleController.inputRunLoopActive());
   deinitPython();
 }