Fix timer management in DEMO-mode

https://github.com/iqb-berlin/testcenter-frontend/issues/358
https://github.com/iqb-berlin/testcenter-frontend/issues/374

src/app/test-controller/routing/unit-route-guards.ts

@@ -60,14 +60,15 @@ export class UnitDeactivateGuard implements CanDeactivate<UnithostComponent> {
     if (!this.tcs.currentMaxTimerTestletId) { // leaving unit is not in a timed block
       return of(true);
     }
-    if (!this.tcs.testMode.forceTimeRestrictions) {
-      return of(true);
-    }
     if (newUnit && newUnit.maxTimerRequiringTestlet && // staying in the same timed block
       (newUnit.maxTimerRequiringTestlet.id === this.tcs.currentMaxTimerTestletId)
     ) {
       return of(true);
     }
+    if (!this.tcs.testMode.forceTimeRestrictions) {
+      this.tcs.interruptMaxTimer();
+      return of(true);
+    }
     const dialogCDRef = this.confirmDialog.open(ConfirmDialogComponent, {
       width: '500px',
       data: <ConfirmDialogData>{