adds a working inventory

lootalot_front/src/components/Chest.vue

@@ -15,7 +15,9 @@
             <PercentInput v-show="is_selling"></PercentInput>
           </div>
           <div v-else-if="perms.canBuy">
-            <button class="button is-danger is-fullwidth" @click="buySelectedItems">Acheter</button>
+            <button class="button is-danger is-fullwidth" 
+              :disabled="selected_items.length == 0"
+              @click="buySelectedItems">Acheter</button>
           </div>
           <div v-else-if="perms.canGrab">
             <button class="button is-static is-fullwidth">Demander</button>