check for workspace command name arg
check for workspace command name arg

* check for workspace command name arg (fix #5131)

For the 'workspace <name> output <output>' command, output_location must
be greater than zero or the attempt to get the workspace name with
join_args will segfault or abort() (depending on the flavor of
sway_assert() in use). This checks and returns an error instead.

* put workspace output error string on one line

To ease grepping as requested

* check for name in workspace gaps command as well

A malformed command here will lead to the same result seen in #5131, so
add a check. Done inside the cmd_workspace_gaps() function itself, to
take advantage of the existing 'Expected...' string.
1ace/sway,1ace/sway,1ace/sway