bug#21262: 25.0.50; Diff-mode gets confused about its narrowing if hunk source not found

[Dima Kogan]

Hi. This bug has been there since at least emacs23 it seems like. To
reproduce:

1. emacs -Q

2. Open any patch file that has hunks from more than one file in it. For
instance, the attached patch file works, but it really doesn't matter

3. Narrow to just the second file's diffs. For instance: M-N M-N C-SPC
C-> C-x n n SPC (last SPC to confirm the narrowing)

4. Try to see the source of the hunk. Move the point to the guts of the
hunk, and M-enter. Emacs asks for the directory where the sources live.
In the process, it changes the narrowing to the wrong hunk. This is
wrong. The narrowing shouldn't change.

5. If we cancel with C-g, the wrong narrowing persists



diff --git a/src/charset.c b/src/charset.c
index b19e344..eeebf17 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -555,7 +555,7 @@ load_charset_map_from_vector (struct charset *charset, 
Lisp_Object vec, int cont
 
   if (len % 2 == 1)
     {
-      add_to_log ("Failure in loading charset map: %V", vec, Qnil);
+      add_to_log ("Failure in loading charset map: %V", vec);
       return;
     }
 
diff --git a/src/image.c b/src/image.c
index 066db74..313419b 100644
--- a/src/image.c
+++ b/src/image.c
@@ -629,16 +629,19 @@ valid_image_p (Lisp_Object object)
 }
 
 
-/* Log error message with format string FORMAT and argument ARG.
+/* Log error message with format string FORMAT and trailing arguments.
    Signaling an error, e.g. when an image cannot be loaded, is not a
    good idea because this would interrupt redisplay, and the error
    message display would lead to another redisplay.  This function
    therefore simply displays a message.  */
 
 static void
-image_error (const char *format, Lisp_Object arg1, Lisp_Object arg2)
+image_error (const char *format, ...)
 {
-  add_to_log (format, arg1, arg2);
+  va_list ap;
+  va_start (ap, format);
+  vadd_to_log (format, ap);
+  va_end (ap);
 }