Prevent `modify-file-local-variable-prop-line' from adding extra ';'

* lisp/files-x.el (modify-file-local-variable-prop-line): Handle
whitespace when checking if there's already a ';' before the
variable (Bug#23294).

Copyright-paperwork-exempt: yes

1 files changed, 3 insertions, 1 deletions

diff --git a/lisp/files-x.el b/lisp/files-x.el
index 2a52792222d..92532e85f4f 100644
--- a/lisp/files-x.el
+++ b/lisp/files-x.el
@@ -377,7 +377,9 @@ from the -*- line ignoring the input argument VALUE."
            ((eq variable 'mode) (goto-char beg))
            ((null replaced-pos) (goto-char end))
            (replaced-pos (goto-char replaced-pos)))
-          (if (and (not (eq (char-before) ?\;))
+          (if (and (save-excursion
+                     (skip-chars-backward " \t")
+                     (not (eq (char-before) ?\;)))
                    (not (equal (point) (marker-position beg)))
                    ;; When existing `-*- -*-' is empty, beg > end.
                    (not (> (marker-position beg) (marker-position end))))