sysupdate: Fix an early return path return value

If the FD has already been opened, return 1 as if opening was
successful, rather than returning 0 as if it gave `ENOENT`.

This fixes doing multiple installdb operations on a single `Context`.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

src/sysupdate/sysupdate-cleanup.c

@@ -57,7 +57,7 @@ static int context_installdb_acquire_fd(Context *c, bool make) {
         assert(c);
 
         if (c->installdb_fd >= 0)
-                return 0;
+                return 1;
 
         _cleanup_free_ char *j = NULL;
         const char *p;