ViewGuard: Fix ctor and assign operator having different behaviours

The difference was very small: The ctor honoured View::inDtor()
while the assign op didn't. It's easy to make them behave the same
by creating a setView() method

As a side-effect the duplicate connect() is also gone now

src/ViewGuard.cpp

@@ -15,13 +15,8 @@
 using namespace KDDockWidgets;
 
 ViewGuard::ViewGuard(View *view)
-    : v(view && view->inDtor() ? nullptr : view)
 {
-    if (v) {
-        m_onDestroy = v->beingDestroyed.connect([this] {
-            v = nullptr;
-        });
-    }
+    setView(view);
 }
 
 ViewGuard::operator bool() const
@@ -53,15 +48,27 @@ View *ViewGuard::view() const
 
 ViewGuard &ViewGuard::operator=(View *view)
 {
-    if (view == v)
-        return *this;
+    setView(view);
+    return *this;
+}
+
+void ViewGuard::setView(View *view)
+{
+    if (view == v)
+        return;
+
+    if (view && view->inDtor()) {
+        // We don't care about views that are already being in DTOR. They count as already deleted for what's ViewGuard concerned.
+        // This is rare anway, would need to require some reentrancy.
+        view = nullptr;
+    }
 
-    // Remove the previous connection
     clear();
     v = view;
 
-    m_onDestroy = v->beingDestroyed.connect([this] {
-        v = nullptr;
-    });
-    return *this;
+    if (v) {
+        m_onDestroy = v->beingDestroyed.connect([this] {
+            v = nullptr;
+        });
+    }
 }

src/ViewGuard.h

@@ -35,6 +35,7 @@ public:
     ViewGuard &operator=(View *);
 
 private:
+    void setView(View *);
     View *v = nullptr;
     KDBindings::ConnectionHandle m_onDestroy;
 };