fix: Prevent crash due to current layout being null

I can't reproduce any crash but it has been seen in the wild.
Doing a code review, I can't find any path for it to be null.

The assert and qWarning will be enough to make a test fail eventually.

src/core/Position.cpp

@@ -183,6 +183,11 @@ void Positions::deserialize(const LayoutSaver::Position &lp)
                 continue; // Skip
             } else {
                 assert(LayoutSaver::Layout::s_currentLayoutBeingRestored);
+                if (!LayoutSaver::Layout::s_currentLayoutBeingRestored) {
+                    /// Doesn't happen, but let's guard it
+                    KDDW_WARN("Positions::deserialize: Current layout is null, report a bug!");
+                    continue;
+                }
                 auto serializedFw =
                     LayoutSaver::Layout::s_currentLayoutBeingRestored->floatingWindowForIndex(
                         index);