Ensure current buffer is version-controlled in vc-region-history

* lisp/vc/vc.el (vc-region-history): Ensure buffer is
version-controlled.  Otherwise if a user runs it in a
non-version-controlled buffer, they get the error:

  Cannot open load file: No such file or directory, vc-nil

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 211feddc55d646562d7b78e300000368b209d12e..b1599915007c99797dbecb9952350f53d7f74e50 100644 (file)
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -2422,6 +2422,8 @@ When called interactively with a prefix argument, prompt for REMOTE-LOCATION."
          (file buffer-file-name)
          (backend (vc-backend file))
          (buf (get-buffer-create "*VC-history*")))
+    (unless backend
+      (error "Buffer is not version controlled"))
     (with-current-buffer buf
       (setq-local vc-log-view-type 'long))
     (vc-call region-history file buf lfrom lto)