Error in logic of certificate generation for RPC

[l0k18]

https://github.com/btcsuite/btcd/blob/master/server.go#L2679

I could be reading this wrong but I think that this should be OR not AND:

		// Generate the TLS cert and key file if both don't already
		// exist.
		if !fileExists(cfg.RPCKey) && !fileExists(cfg.RPCCert) {
			err := genCertPair(cfg.RPCCert, cfg.RPCKey)
			if err != nil {
				return nil, err
			}
		}

In the current state of the code, if either file exists but the other doesn't, it won't generate a new one, but the RPC will not have the necessary, inseparable pair of keys to work with.

It should either flag a terminal error or assume a non atomic write occurred and overwrite the two files.