fix bugs of depth related to recursively rule calling

[after12am]

testing codes is:

patter1

corner
rule corner md 4 {
  { s 1 2 1.2 }ARC
  {ry 36}corner
}
rule ARC md 3 {
  { z 0.85 rx 4.5 s 0.95 } ARC
  box
}

pattern2

crate
rule crate md 2 {
  box
  { s 0.5 x 0.9 z 0.9 y -0.9 } crate //1
  { s 0.5 x -0.9 z 0.9 y -0.9 } crate //2
}