affile: remove null pointer dereference in affile_dd_reuse_writer()`

In very rare (and unrealistic) cases syslog-ng could crash if it was
reloaded and it was unable to reuse it's file writers.

Signed-off-by: Szilárd Parrag <szilard.parrag@gmail.com>

modules/affile/affile-dest.c

@@ -292,24 +292,28 @@ static void
 affile_dw_set_owner(AFFileDestWriter *self, AFFileDestDriver *owner)
 {
   GlobalConfig *cfg = log_pipe_get_config(&owner->super.super.super);
+  log_pipe_set_config(&self->super, cfg);
+
+  if (self->writer)
+    log_pipe_set_config((LogPipe *) self->writer, cfg);
 
   if (self->owner)
     log_pipe_unref(&self->owner->super.super.super);
-  log_pipe_ref(&owner->super.super.super);
+
+
   self->owner = owner;
-  self->super.expr_node = owner->super.super.super.expr_node;
+  if (self->owner) {
+    log_pipe_ref(&self->owner->super.super.super);
+    log_pipe_set_options(&self->super, &self->owner->super.super.super.options);
+    self->super.expr_node = self->owner->super.super.super.expr_node;
+  }
 
-  log_pipe_set_options(&self->super, &owner->super.super.super.options);
-  log_pipe_set_config(&self->super, cfg);
-  if (self->writer)
-    {
-      log_pipe_set_config((LogPipe *) self->writer, cfg);
+  if (self->writer && self->owner)
       log_writer_set_options(self->writer,
                              &self->super,
                              &owner->writer_options,
                              self->owner->super.super.id,
                              self->filename);
-    }
 }
 
 static void