ftp: Ensure to include command in Curl_ftpsend() sendbuffer #2985
Commit 8238ba9 inadvertently removed the actual command to be sent from the send buffer in a refactoring. Add back copying the command into the buffer. Also add more guards against malformed input while at it. There seems to be a lack of testing of this module, but I'm not really sure how to improve that right now so I'll leave that for another PR.
Also comes with a bonus tiny memleak fix in krb5.c which was the original reason for spotting this.