fix #8602 -- opening a file ending in .ipynb~ (NOT THE TILDE) causes a crash

Author: williamstein

src/packages/frontend/file-editors.ts

@@ -4,7 +4,7 @@
  */
 
 import {
-  filename_extension_notilde,
+  filename_extension,
   meta_file,
   path_split,
   defaults,
@@ -148,7 +148,7 @@ function get_ed(
   ext =
     ext ??
     altExt[key(project_id, path)] ??
-    filename_extension_notilde(path).toLowerCase();
+    filename_extension(path).toLowerCase();
 
   // either use the one given by ext, or if there isn't one, use the '' fallback.
   const spec =

src/packages/frontend/project/open-file.ts

@@ -17,7 +17,6 @@ import { retry_until_success } from "@cocalc/util/async-utils";
 import {
   defaults,
   filename_extension,
-  filename_extension_notilde,
   path_to_tab,
   required,
   uuid,
@@ -173,7 +172,7 @@ export async function open_file(
   } catch (_) {
     // TODO: old projects will not have the new realpath api call -- can delete this try/catch at some point.
   }
-  let ext = opts.ext ?? filename_extension_notilde(opts.path).toLowerCase();
+  let ext = opts.ext ?? filename_extension(opts.path).toLowerCase();
 
   // Next get the group.
   let group: string;