In some cases a TypeError is generated when user presses the load annotation button when there are no annotations.

What does this Pull Request do?

Provides a conditional to check whether a variable is defined before proceeding with loading annotations.

How should this be tested?

Before pulling the changes, create a new basic image object. Open you browser console. Before making any annotations, press the toggle annotation button (load annotation button). You should see a TypeError around line 122 of base.js.
Pull the changes in this pull-request. Clear your caches as appropriate.
Create a basic image.
Open your browser console. Before annotating the basic image object, press the toggle annotation button. In the console you should no longer see the TypeError seen previously.