fix(hg): guard against missing file_info entry for unresolved files

Initialise the file_info entry before setting status when the file
state is 'u' (unresolved), preventing a nil index error in
tracked_files().

Cherry-picked from cavanaug/diffview.nvim (commit 2711fc7).

Author: cavanaug

lua/diffview/vcs/adapters/hg/init.lua

@@ -1140,6 +1140,14 @@ HgAdapter.tracked_files = async.wrap(function (self, left, right, args, kind, op
       end
     end
     if file.state == 'u' then
+      -- Ensure file_info entry exists before accessing it
+      if not file_info[file.path] then
+        file_info[file.path] = {
+          status = "",
+          name = file.path,
+          stats = {},
+        }
+      end
       file_info[file.path].status = 'U'
       file_info[file.path].base = base
       if file.other_path ~= file.path then