Do not tokenize empty input.

src/libmime/filter.c

@@ -801,7 +801,10 @@ classifiers_callback (gpointer value, void *arg)
 			}
 			cur = g_list_next (cur);
 		}
-		g_hash_table_insert (task->tokens, cl->tokenizer, tokens);
+
+		if (tokens != NULL) {
+			g_hash_table_insert (task->tokens, cl->tokenizer, tokens);
+		}
 	}
 
 	/* Take care of subject */

src/tokenizers/osb.c

@@ -49,6 +49,10 @@ osb_tokenize_text (struct tokenizer *tokenizer,
 	gint i, processed = 0;
 	guint w;
 
+	if (input == NULL) {
+		return FALSE;
+	}
+
 	if (*tree == NULL) {
 		*tree = g_tree_new (token_node_compare_func);
 		rspamd_mempool_add_destructor (pool,