Fix: crash due to dangling DbAccessor

lua/kagiroi/kagiroi_dict.lua

@@ -40,6 +40,7 @@ function Module.release()
         return
     end
     if Module.dic_db and Module.dic_db:loaded() then
+        collectgarbage()
         Module.dic_db:close()
     end
 end

lua/kagiroi/kagiroi_viterbi.lua

@@ -425,6 +425,7 @@ function Module.init()
 end
 
 function Module.fini()
+    Module.lattice = nil
     Module.kagiroi_dict.release()
 end
 

tests/kagiroi.test.yaml

@@ -40,3 +40,10 @@ deploy:
     tests:
       - send: 'aida{Control+c}'
         assert: cand[1].text == "あいだ" and cand[2].text == "アイダ" and cand[3].text == "ｱｲﾀﾞ"
+
+  nocrash:
+    tests:
+      - send: nani{space}
+        assert: true
+      - send: nani{space}
+        assert: true