Exclude directions exist in upper inner char on lower inner char

Upper char has higher priority in deciding the result of crossing

Before

┏━━━━━━━━┓         
┃        ┃         
┃        ┌────────┐
┃        │        │
┃        │        │
┗━━━━━━━━│        │
         │        │
         └────────┘

After

┏━━━━━━━━┓         
┃        ┃         
┃        ┞────────┐
┃        │        │
┃        │        │
┗━━━━━━━━┥        │
         │        │
         └────────┘

tuanchauict / MonoSketch

Exclude directions exist in upper inner char on lower inner char #590