LibWeb: Log error instead of crashing if stacking context painted twice

Turns out this mistake happens fairly often, so it is more preferable to
log message and proceed instead of crashing.

Userland/Libraries/LibWeb/Painting/StackingContext.cpp

@@ -57,7 +57,9 @@ void StackingContext::sort()
 
 void StackingContext::set_last_paint_generation_id(u64 generation_id)
 {
-    VERIFY(!m_last_paint_generation_id.has_value() || m_last_paint_generation_id.value() < generation_id);
+    if (m_last_paint_generation_id.has_value() && m_last_paint_generation_id.value() >= generation_id) {
+        dbgln("FIXME: Painting commands are recorded twice for stacking context: {}", m_paintable->layout_node().debug_description());
+    }
     m_last_paint_generation_id = generation_id;
 }