MFC r337779:

tftp: Close a resource leak when putting files

Reported by: Coverity
CID: 1394842

MFC r336609:

Fix several Coverity warnings in tftp

Some of the changes are in the libexec/tftpd directory, but to functions that
are only used by tftp(1) (they share some code).

* strcpy => strlcpy (1006793, 1006794, 1006796, 1006741)
* Unchecked return value and TOCTTOU (1009314)
* NULL pointer dereference (1018035, 1018036)

Reported by: Coverity
CID: 1006793, 1006794, 1006796, 1006741, 1009314, 1018035
CID: 1018036

MFC r287320:
- uri is expected to be nul-terminated (strchr used later),
so use strlcpy instead of strncpy.
- replace the other two cases of strncpy+\0 with strlcpy.

MFC r287320:
- uri is expected to be nul-terminated (strchr used later),
so use strlcpy instead of strncpy.
- replace the other two cases of strncpy+\0 with strlcpy.