bo-src/bo-src-i works not the same as ng-src

[Semigradsky]

<img ng-src='{{imageUrl}}'>

if imageUrl undefined we get:

<img ng-src=''>

---

For bo-src we get:

<img bo-src='imageUrl' src=''>

For bo-src-i:

<img bo-src-i='' src=''>

We are left with an empty src attribute.