Work around code studio errors when unable to fetch channel data
Work around code studio errors when unable to fetch channel data

Since I don't have AWS credentials yet, fetching the source files
fails. This failure wasn't being handled well in the frontend code,
causing the all of applab to not load.

This change sets a default empty source file when you can't fetch
the actual one.

rvarshney/code-dot-org,dillia23/code-dot-org,dillia23/code-dot-org,pickettd/code-dot-org,dillia23/code-dot-org,rvarshney/code-dot-org,rvarshney/code-dot-org,pickettd/code-dot-org,dillia23/code-dot-org,pickettd/code-dot-org,rvarshney/code-dot-org,pickettd/code-dot-org,dillia23/code-dot-org,rvarshney/code-dot-org,rvarshney/code-dot-org,pickettd/code-dot-org,pickettd/code-dot-org,pickettd/code-dot-org,rvarshney/code-dot-org,dillia23/code-dot-org,pickettd/code-dot-org,dillia23/code-dot-org,rvarshney/code-dot-org,dillia23/code-dot-org