Have Text.pane return nothing for a header instead of trapping

A column's or the workspace's tag has no pane, and asking one for it hit
unreachable; every caller guarded against that by checking `what` first.
An optional makes each caller say what it does without a pane, so a
forgotten guard no longer compiles into a crash.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/File.zig b/src/File.zig
index 262f3ebb..af538385 100644
--- a/src/File.zig
+++ b/src/File.zig
@@ -655,7 +655,7 @@ pub fn cursorLines(arena: std.mem.Allocator, pane: *Pane, f: *State) ![]const []
 /// Edit-buffer fragments and other temporary text retain modal's scan path.
 fn contentIndex(t: *Text, text: []const u8) ?[]const usize {
     if (t.what != .body) return null;
-    const pane = t.pane();
+    const pane = t.pane() orelse return null;
     const f = if (pane.file) |*file| file else return null;
     if (text.ptr != f.content.ptr or text.len != f.content.len) return null;
     return lineIndex(pane.gpa, f) catch null;