engine: reset version on fetch error

client/src/plugins/engine.js

@@ -1,4 +1,3 @@
-
 export default (context, inject) => {
   const { store, $axios } = context
 
@@ -18,6 +17,7 @@ export default (context, inject) => {
         if (status >= 500) {
           console.warn(`HTTP ${status} ${statusText}`)
           delay = 5000
+          store.commit('engine/setVersion', -1)
         }
       }
 

client/src/store/engine.js

@@ -7,5 +7,8 @@ export const mutations = {
   setJson(state, json) {
     state.json = json
     state.version = parseInt(json.version, 10)
-  }
+  },
+  setVersion(state, version) {
+    state.version = version
+  },
 }