Completion of error handling

[elfring]

Would you like to add more error handling for return values from functions like the following?

• malloc ⇒ makeHeader
• strdup ⇒ makeRule

[gpakosz]

Hello @elfring 👋

I think you should report that to upstream: https://www.piumarta.com/software/peg/

I do not intend to maintain a fork. Just a mirror.