forked from viewit/OrcaSlicer-KX
1. fix possible empty layers (caused by continues walls) 2. fix normal node may be absorbed in drop_nodes in "tree hybrid" 3. popup message to ask the user to select best parameters for tree strong and tree hybrid. 4. auto select lightning infill for tree hybrid. Change-Id: I7d172887a9b0e4f268267684e83fc02dc7ec6a0c (cherry picked from commit bc6d130e86c252d7fc1f84c4df7da95050dd5d51)