Fix panic when using surround_replace/delete (#9796)

1. Create a document containing `{A}`
1. C-w v # vsplit
1. gl    # goto_line_end
1. b     # move_prev_word_start
1. `     # switch_to_lowercase
1. mrm(  # surround replace
1. C-w v # vsplit

In the debug build surround_replace/delete will immedately assert with
`assertion failed: last <= from', transaction.rs:597:13`. The splits and
lowercase conversion are not needed to trigger the bug.

In the release build the surround becomes `)a(` and the last vsplit
causes the transaction to panic.
`internal error: entered unreachable code:
(Some(Retain(18446744073709551573)))', transaction.rs:185:46`

Since the selection direction is backwards get_surround_pos returns the
pairs reversed but the downstream code assumes they are in the forward
direction.

1 files changed, 2 insertions, 1 deletions

diff --git a/helix-core/src/surround.rs b/helix-core/src/surround.rs
index b96cce5a..513f8749 100644
--- a/helix-core/src/surround.rs
+++ b/helix-core/src/surround.rs
@@ -260,7 +260,8 @@ pub fn get_surround_pos(
         if change_pos.contains(&open_pos) || change_pos.contains(&close_pos) {
             return Err(Error::CursorOverlap);
         }
-        change_pos.extend_from_slice(&[open_pos, close_pos]);
+        // ensure the positions are always paired in the forward direction
+        change_pos.extend_from_slice(&[open_pos.min(close_pos), close_pos.max(open_pos)]);
     }
     Ok(change_pos)
 }