Why does Atticus welcome Dill instead of getting mad at him for running away?

In chapter 14, Scout finds Dill hiding under her bed. As the children don't want to snitch on each other, Scout finds a pan of cornbread and some milk for him without telling Atticus. Jem allows Dill to eat and explain how he traveled from Meridian to Maycomb before he goes and tells Atticus. When Atticus does appear at Scout's bedroom, his first response is the following:

"Scout, we can do better than a pan...

In chapter 14, Scout finds Dill hiding under her bed. As the children don't want to snitch on each other, Scout finds a pan of cornbread and some milk for him without telling Atticus. Jem allows Dill to eat and explain how he traveled from Meridian to Maycomb before he goes and tells Atticus. When Atticus does appear at Scout's bedroom, his first response is the following:

"Scout, we can do better than a pan of cold cornbread, can't we? You fill this fellow up and when I get back we'll see what we can see" (141).

Atticus welcomes Dill rather than getting angry because he's not one to panic, he's a kind person, and scaring a little boy with an angry lecture might cause him to run off again. As a father, Atticus knows that Dill needs to stay put while he contacts his Aunt, Miss Rachel, who will then call his mother to let her know that he is fine. There's no need to lose one's head over the situation as long as Dill is safe and sound. 

Dill threatens with a pleading voice that he will run off again if Atticus tells his Aunt Rachel where he is, but Atticus doesn't fall for this. He tells Dill he's just going over to tell Aunt Rachel that he will be staying the night with them. Then he tells him "And for goodness' sake put some of the county back where it belongs, the soil erosion's bad enough as it is" (141). Scout informs him that this means he needs to take a bath. 

Atticus handles the situation perfectly by being a kind host, calming the boy down, adding a bit a humor, and letting Dill's family know where he is. Again, if Atticus had gotten angry, Dill probably would have run away again and then it really would be time to panic.