Fix temp dir creation when TMPDIR is set and has no trailing slash

[pschmitt]

TMPDIR when set usually does not include a trailing slash.

This here fixes the tmpdir creation when editing the current cmdline, which leads to the following when TMPDIR doesn't end with /:

> my-very-long-command
# bindkey for editing the command line
mktemp: failed to create file via template ‘/tmpzshXXXXXX’: Permission denied

zvm_vi_edit_command_line:7: no such file or directory:

Having a static / in the tmpdir filename works in both cases since /tmp//zvm is the same as /tmp/zvm

[jeffreytse]

Hi @pschmitt, thanks for the contribution to compatibility improvement. 👍

[pschmitt]

Sure thing. Anything holding you back from merging this one in?

[jeffreytse]

@pschmitt Recently I'm quite busy, sorry for the late reply. : )