Don't use large file check in buffers already in fundamental-mode.

This change will prevent unnecessary requests to literally open files that are
literal already (like elfeed's index file).

CHANGELOG.develop

@@ -1000,6 +1000,8 @@ Other:
   - Key bindings (thanks to bb2020)
     - ~SPC-j-C~ to =check-parens=
     - ~SPC-,~ to =goto-last-change=
+  - Excluded =fundamental-mode= from =spacemacs/check-large-file=
+    (thanks to Alexander Miller)
 *** Layer changes and fixes
 **** Alda
 - Key bindings:

layers/+spacemacs/spacemacs-defaults/funcs.el

@@ -89,7 +89,7 @@ Only modes that don't derive from `prog-mode' should be listed here."
 (defcustom spacemacs-large-file-modes-list
   '(archive-mode tar-mode jka-compr git-commit-mode image-mode
                  doc-view-mode doc-view-mode-maybe ebrowse-tree-mode
-                 pdf-view-mode)
+                 pdf-view-mode fundamental-mode)
   "Major modes which `spacemacs/check-large-file' will not be
 automatically applied to."
   :group 'spacemacs