prevent panic when parsing incomplete multi-expr (|) matches (#15230)

Fixes #14971, fixes #15229

# User-Facing Changes

Fixes a panic when variable data is accessed after invalid usage of the
`|` separator, which made it impossible to type certain match arms:

```nushell
> match $in { 1 |
Error:   x Main thread panicked.
  |-> at crates/nu-protocol/src/engine/state_delta.rs💯14
  `-> internal error: missing required scope frame
```

# Description

Removes duplicative calls to `exit_scope` from an inner loop when `|`
parse errors are encountered. The outer loop creates and exits scopes
for each match arm.

crates/nu-command/tests/commands/match_.rs

@@ -244,6 +244,13 @@ fn match_with_guard_no_expr_after_if() {
     assert!(actual.err.contains("Match guard without an expression"));
 }
 
+#[test]
+fn match_with_or_missing_expr() {
+    let actual = nu!("match $in { 1 | }");
+
+    assert!(actual.err.contains("expected pattern"));
+}
+
 #[test]
 fn match_with_comment_1() {
     Playground::setup("match_with_comment", |dirs, _| {

crates/nu-parser/src/parser.rs

@@ -4680,8 +4680,6 @@ pub fn parse_match_block_expression(working_set: &mut StateWorkingSet, span: Spa
                         "end of input".into(),
                         Span::new(output[position - 1].span.end, output[position - 1].span.end),
                     ));
-
-                    working_set.exit_scope();
                     break;
                 }
 
@@ -4695,8 +4693,6 @@ pub fn parse_match_block_expression(working_set: &mut StateWorkingSet, span: Spa
                         "end of input".into(),
                         Span::new(output[position - 1].span.end, output[position - 1].span.end),
                     ));
-
-                    working_set.exit_scope();
                     break;
                 } else {
                     connector = working_set.get_span_contents(output[position].span);