Opening the wrong file leads to long wait time

[jmmunoz14]

Is your feature request related to a problem? Please describe.
If you are browsing the source code of a repository and you open a file which you didn’t intend to open, the app is completely frozen until it loads or you force close it. This also happens with file extensions which are clearly not supposed to be viewed (such as pdfs, wavs, mp4s, etc).

Describe the solution you'd like
A way to stop the load of any file that is not supposed to be open, a simple “Cancel” button while loading.

Describe alternatives you've considered
A cancel button on the loading screen and a check on file extensions which are not supported by SwiftHub.

Additional context
Add any other context or screenshots about the feature request here.