This function attempts to return the first available restart with the string "muffle" in its name. If the condition is an error, it will attempt to find the first restart named "return_error" (used internally in catchr to return a NULL
value). If the condition is an "interrupt", it will attempt to find the first restart named "resume". If no such restarts can be found, it returns NULL
.
first_muffle_restart(cond)
A condition
A restart or NULL
if none can be found.