Inconsistent and/or incorrect behaviour of the `-m|--pem` flag

[cyqsimon]

The -m|--pem flag causes some unexpected interactions with other flags.
The following is a table of the expected behaviour and the actual behaviour (of dump and connect, respectively):

	Expected	dump	connect
--pem --json	Fail fast ❔	Prints chain PEM ❔	Prints chain PEM, followed by JSON with .certificates array emptied ❌
--pem --first	Prints leaf PEM	Prints leaf PEM ✔️	Prints chain PEM ❌
--pem --json --first	Fail fast ❔	Prints leaf PEM ❔	Prints chain PEM, followed by JSON with .certificates array emptied ❌

For the question marked fields, I personally would expect them to fail fast because I consider --pem and --json to be semantically conflicting flags, but I will acknowledge that other design decisions may also be valid. The red cross fields are however most certainly incorrect.