bug#28708: 27.0.50; [PATCH] Fix search for ~/.Xdefaults-HOSTNAME

[Johan Bockgård]

Emacs is supposed to look for X resources in ~/.Xdefaults-HOSTNAME, but
the code forgets the hyphen in the filename.

The bug was introduced in Emacs 25.1, by commit
1e6879dbdb0832427f5c588c89a53a8a80768a00:

2014-12-25  Paul Eggert  <eggert@cs.ucla.edu>

       Prefer stpcpy to strcat ...


**

The patch (should this go in the emacs-26 branch?):


diff --git a/src/xrdb.c b/src/xrdb.c
index 15a0147..3c1bad1 100644
--- a/src/xrdb.c
+++ b/src/xrdb.c
@@ -345,6 +345,7 @@ get_user_db (Display *display)
     db = XrmGetStringDatabase (xdefs);
   else
     {
+      /* Use ~/.Xdefaults.  */
       char *home = gethomedir ();
       ptrdiff_t homelen = strlen (home);
       char *filename = xrealloc (home, homelen + sizeof xdefaults);
@@ -375,13 +376,15 @@ get_environ_db (void)
 
   if (!p)
     {
+      /* Use ~/.Xdefaults-HOSTNAME.  */
       char *home = gethomedir ();
       ptrdiff_t homelen = strlen (home);
       Lisp_Object system_name = Fsystem_name ();
       ptrdiff_t filenamesize = (homelen + sizeof xdefaults
-                               + SBYTES (system_name));
+                               + 1 + SBYTES (system_name));
       p = filename = xrealloc (home, filenamesize);
-      lispstpcpy (stpcpy (filename + homelen, xdefaults), system_name);
+      lispstpcpy (stpcpy (stpcpy (filename + homelen, xdefaults), "-"),
+                 system_name);
     }
 
   db = XrmGetFileDatabase (p);