added dwindle:no_gaps_when_only

src/layout/DwindleLayout.hpp

@@ -30,6 +30,8 @@ struct SDwindleNodeData {
 
     float           splitRatio = 1.f;
 
+    bool            valid = true;
+
     // For list lookup
     bool operator==(const SDwindleNodeData& rhs) {
         return pWindow == rhs.pWindow && workspaceID == rhs.workspaceID && position == rhs.position && size == rhs.size && pParent == rhs.pParent && children[0] == rhs.children[0] && children[1] == rhs.children[1];