Fix panels disappearing when selecting a-videosphere entity

[vincentfretin]

backport changes from aframevr/aframe-inspector#680
This probably may not be an issue in 3dstreet because you don't use video texture yet, but who knows in the future you may so better to backport all the fixes I did in aframe-inspector.

Note in this part of the code you had a change where you added a condition line 155 in new code, I kept it.

      if (typeof value === 'string') {
        url = AFRAME.utils.srcLoader.parseUrl(value);
      }