fix #29. amount value always positive

src/components/BalanceAddBody.vue

@@ -22,7 +22,7 @@
   </div>
 </template>
 <script lang="ts">
-import { defineComponent, ref, PropType, computed } from 'vue';
+import { defineComponent, ref, PropType, computed, watch } from 'vue';
 import { useBalanceStore } from '../store';
 import { hasPermission, useUserStore } from '@flaschengeist/api';
 import PERMISSIONS from '../permissions';
@@ -58,6 +58,9 @@ export default defineComponent({
         ? <FG.User>props.user
         : <FG.User>userStore.users.find((a) => a.userid === <string>props.user)
     );
+    watch(amount, (a) => {
+      amount.value = Math.abs(a);
+    });
     return { changeBalance, addShortcut, canAddCredit, amount };
   },
 });