* refactor module cleanup (also fixes double-free)

src/backend.c

@@ -110,11 +110,24 @@ f2b_backend_init(f2b_backend_t *backend, f2b_config_section_t *config) {
   if (dlerr)
     f2b_log_msg(log_error, "backend load error: %s", dlerr);
   if (backend->h) {
-    if (backend->cfg && backend->destroy)
+    if (backend->cfg && backend->destroy) {
       backend->destroy(backend->cfg);
+      backend->cfg = NULL;
+    }
     dlclose(backend->h);
+    backend->create  = NULL;
+    backend->config  = NULL;
+    backend->state   = NULL;
+    backend->logcb   = NULL;
+    backend->start   = NULL;
+    backend->stop    = NULL;
+    backend->ping    = NULL;
+    backend->ban     = NULL;
+    backend->unban   = NULL;
+    backend->check   = NULL;
+    backend->destroy = NULL;
+    backend->h       = NULL;
   }
-  free(backend);
   return false;
 }
 

src/filter.c

@@ -176,11 +176,22 @@ f2b_filter_init(f2b_filter_t *filter, f2b_config_section_t *config) {
   if (dlerr)
     f2b_log_msg(log_error, "filter load error: %s", dlerr);
   if (filter->h) {
-    if (filter->cfg && filter->destroy)
+    if (filter->cfg && filter->destroy) {
       filter->destroy(filter->cfg);
+      filter->cfg = NULL;
+    }
     dlclose(filter->h);
+    filter->create  = NULL;
+    filter->config  = NULL;
+    filter->append  = NULL;
+    filter->logcb   = NULL;
+    filter->state   = NULL;
+    filter->flush   = NULL;
+    filter->stats   = NULL;
+    filter->match   = NULL;
+    filter->destroy = NULL;
+    filter->h       = NULL;
   }
-  free(filter);
   return false;
 }
 

src/source.c

@@ -106,11 +106,22 @@ f2b_source_init(f2b_source_t *source, f2b_config_section_t *config) {
   if (dlerr)
     f2b_log_msg(log_error, "source load error: %s", dlerr);
   if (source->h) {
-    if (source->cfg && source->destroy)
+    if (source->cfg && source->destroy) {
       source->destroy(source->cfg);
+      source->cfg = NULL;
+    }
     dlclose(source->h);
+    source->create  = NULL;
+    source->config  = NULL;
+    source->state   = NULL;
+    source->logcb   = NULL;
+    source->start   = NULL;
+    source->next    = NULL;
+    source->stats   = NULL;
+    source->stop    = NULL;
+    source->destroy = NULL;
+    source->h       = NULL;
   }
-  free(source);
   return false;
 }