fix 3 bugs

[wlsnx]

1. zellij/zellij-server/src/panes/tiled_panes/tiled_pane_grid.rs

   Lines 1168 to 1178 in 3da1cbf

   	pub fn split(direction: SplitDirection, rect: &PaneGeom) -> Option<(PaneGeom, PaneGeom)> {
   	let space = match direction {
   	SplitDirection::Vertical => rect.cols,
   	SplitDirection::Horizontal => rect.rows,
   	};
   	if let Some(p) = space.as_percent() {
   	let first_rect = match direction {
   	SplitDirection::Vertical => PaneGeom {
   	cols: Dimension::percent(p / 2.0),
   	..*rect
   	},

   first_rect.cols.inner == 1.
   Between split_vertically() and relayout(), there is a change_size() call. New pane usually has a frame,so get_content_columns() returns 0, change_size() is skipped.
   However if you set pane_frames false and vertically split the right most pane, get_content_columns() returns 1.change_size() calls drain_until(1) for each row.
   Finally, drain_until(1) discard first widechar and all characters behind it.

2. ZELLIJ_SOCK_DIR.join(name) should be a valid filename in directory ZELLIJ_SOCK_DIR,so name cannot equals to "." or "..", as well as contains '/'.

3. zellij -s '' Session name cannot be empty. Please provide a specific session name.
   zellij attach --create '' Panic occured: called Result::unwrap() on an Err value: Os { code: 98, kind: AddrInUse, message: "Address already in use" }

[imsnif]

Hey @wlsnx - thanks for looking into these. I do not understand the user facing impact of 1. Can you please explain it from the point of view of the user? What bug is this solving?

[wlsnx]

https://www.youtube.com/watch?v=E95MuYAxYnM
After split vertically, wide characters (Chinese, emojis, etc.) disappeared.

[wlsnx]

@imsnif This happens only if you set pane_frames false and vertically split the right most pane.

[imsnif]

Great work on all of these, @wlsnx ! I added a comment to the drain_until function to explain the new conditional.