fix skill deadlock after trying to move into a character

lib/spellbook.lua

@@ -28,11 +28,14 @@ local walk = setmetatable({
 function walk:cast(caster, target)
     if not caster:try(Tree.behaviors.stats, function(stats)
             return stats.mana >= 2
-    end) then return false end
+        end) then
+        return false
+    end
 
     local path = self.path
-    if path:is_empty() then return false end
     path:pop_front()
+    if path:is_empty() then return false end
+
     for p in path:values() do print(p) end
     caster:has(Tree.behaviors.map):followPath(path, function()
         caster:has(Tree.behaviors.spellcaster):endCast()