fix regression of position

close violentmonkey/violentmonkey#111

src/background/app.js

@@ -216,6 +216,9 @@ vmdb.initialized.then(() => {
   });
   setTimeout(autoUpdate, 2e4);
   sync.initialize();
+
+  // XXX fix position regression in v2.6.3
+  vmdb.checkPosition();
 });
 
 // Common functions

src/background/utils/db.js

@@ -7,14 +7,14 @@ let db;
 
 const position = {
   value: 0,
-  set(number) {
-    position.value = number;
+  set(v) {
+    position.value = +v || 0;
   },
   get() {
-    return position + 1;
+    return position.value + 1;
   },
-  update(value) {
-    if (position.value < value) position.value = value;
+  update(v) {
+    if (position.value < +v) position.set(v);
   },
 };