Fix a couple of problems in changelog generating functions

* lisp/vc/diff-mode.el (diff-add-log-current-defuns): If there is a
scan-error when calling end-of-defun, go to end of hunk.  This can
easily happen since we are calling end-of-defun on a partial code
fragment from a diff.
* lisp/vc/log-edit.el (log-edit-generate-changelog-from-diff): Bind
display-buffer-overriding-action around the log-edit-show-diff call
only.  Otherwise, it can affect, for example, debugger windows
triggered by the diff-add-log-current-defuns call.

Author: npostavs

lisp/vc/diff-mode.el

@@ -2247,29 +2247,32 @@ The elements of the alist are of the form (FILE . (DEFUN...)),
 where DEFUN... is a list of function names found in FILE."
   (save-excursion
     (goto-char (point-min))
-    (let ((defuns nil)
-          (hunk-end nil)
-          (hunk-mismatch-files nil)
-          (make-defun-context-follower
-           (lambda (goline)
-             (let ((eodefun nil)
-                   (defname nil))
-               (list
-                (lambda () ;; Check for end of current defun.
-                  (when (and eodefun
-                             (funcall goline)
-                             (>= (point) eodefun))
-                    (setq defname nil)
-                    (setq eodefun nil)))
-                (lambda (&optional get-current) ;; Check for new defun.
-                  (if get-current
-                      defname
-                    (when-let* ((def (and (not eodefun)
-                                          (funcall goline)
-                                          (add-log-current-defun)))
-                                (eof (save-excursion (end-of-defun) (point))))
-                      (setq eodefun eof)
-                      (setq defname def)))))))))
+    (let* ((defuns nil)
+           (hunk-end nil)
+           (hunk-mismatch-files nil)
+           (make-defun-context-follower
+            (lambda (goline)
+              (let ((eodefun nil)
+                    (defname nil))
+                (list
+                 (lambda () ;; Check for end of current defun.
+                   (when (and eodefun
+                              (funcall goline)
+                              (>= (point) eodefun))
+                     (setq defname nil)
+                     (setq eodefun nil)))
+                 (lambda (&optional get-current) ;; Check for new defun.
+                   (if get-current
+                       defname
+                     (when-let* ((def (and (not eodefun)
+                                           (funcall goline)
+                                           (add-log-current-defun)))
+                                 (eof (save-excursion
+                                        (condition-case ()
+                                            (progn (end-of-defun) (point))
+                                          (scan-error hunk-end)))))
+                       (setq eodefun eof)
+                       (setq defname def)))))))))
       (while
           ;; Might need to skip over file headers between diff
           ;; hunks (e.g., "diff --git ..." etc).

lisp/vc/log-edit.el

@@ -788,18 +788,20 @@ This command will generate a ChangeLog entries listing the
 functions.  You can then add a description where needed, and use
 \\[fill-paragraph] to join consecutive function names."
   (interactive)
-  (let* ((diff-buf nil)
-         ;; Unfortunately, `log-edit-show-diff' doesn't have a NO-SHOW
-         ;; option, so we try to work around it via display-buffer
-         ;; machinery.
-         (display-buffer-overriding-action
-          `(,(lambda (buf alist)
-               (setq diff-buf buf)
-               (display-buffer-no-window buf alist))
-            . ((allow-no-window . t)))))
-    (change-log-insert-entries
-     (with-current-buffer (progn (log-edit-show-diff) diff-buf)
-       (diff-add-log-current-defuns)))))
+  (change-log-insert-entries
+   (with-current-buffer
+       (let* ((diff-buf nil)
+              ;; Unfortunately, `log-edit-show-diff' doesn't have a
+              ;; NO-SHOW option, so we try to work around it via
+              ;; display-buffer machinery.
+              (display-buffer-overriding-action
+               `(,(lambda (buf alist)
+                    (setq diff-buf buf)
+                    (display-buffer-no-window buf alist))
+                 . ((allow-no-window . t)))))
+         (log-edit-show-diff)
+         diff-buf)
+     (diff-add-log-current-defuns))))
 
 (defun log-edit-insert-changelog (&optional use-first)
   "Insert a log message by looking at the ChangeLog.