layout: fix null deref in focalPointForDir and moveInDirection (#13652)

Added a guard against expired m_parent weak pointer in IModeAlgorithm::focalPointForDir
when the fullscreen monitor path is taken, and also added a null check in
CLayoutManager::moveInDirection. This seemed to have fixed a segfault triggered
by a 3-finger swipe gesture end on a fullscreen tiled window.

1 files changed, 15 insertions, 2 deletions

diff --git a/src/layout/algorithm/ModeAlgorithm.cpp b/src/layout/algorithm/ModeAlgorithm.cpp
index dea5bb17..2fea2b68 100644
--- a/src/layout/algorithm/ModeAlgorithm.cpp
+++ b/src/layout/algorithm/ModeAlgorithm.cpp
@@ -18,8 +18,21 @@ std::optional<Vector2D> IModeAlgorithm::predictSizeForNewTarget() {
 std::optional<Vector2D> IModeAlgorithm::focalPointForDir(SP<ITarget> t, Math::eDirection dir) {
     Vector2D   focalPoint;
 
-    const auto WINDOWIDEALBB =
-        t->fullscreenMode() != FSMODE_NONE ? m_parent->space()->workspace()->m_monitor->logicalBox() : t->window()->getWindowIdealBoundingBoxIgnoreReserved();
+    const auto getFullscreenBB = [&]() -> std::optional<CBox> {
+        const auto PARENT = m_parent.lock();
+        if (!PARENT)
+            return std::nullopt;
+        const auto SPACE = PARENT->space();
+        if (!SPACE)
+            return std::nullopt;
+        const auto WS = SPACE->workspace();
+        if (!WS || !WS->m_monitor)
+            return std::nullopt;
+        return WS->m_monitor->logicalBox();
+    };
+
+    const auto WINDOWIDEALBB = t->fullscreenMode() != FSMODE_NONE ? getFullscreenBB().value_or(t->window()->getWindowIdealBoundingBoxIgnoreReserved()) :
+                                                                    t->window()->getWindowIdealBoundingBoxIgnoreReserved();
 
     switch (dir) {
         case Math::DIRECTION_UP: focalPoint = WINDOWIDEALBB.pos() + Vector2D{WINDOWIDEALBB.size().x / 2.0, -1.0}; break;