fix: prevent fatal error when browser failed to start

[syavorsky]

fixes #20

This is just a workaround, I guess onBrowserComplete normally should never be called multiple times for same browser. Grunt won't fail at least if it happens so.

[vojtajina]

Thanks @yavorskiy. Do you understand how can this happen? I would much rather fix this in Karma than working it around in the reporter.

[vojtajina]

It looks like it's related to the syntax error. If there is an error during loading a file, Karma should report error() and complete() and not even start the run. For some reason it does start the run and calls complete twice.

[syavorsky]

@vojtajina right that's exactly the reason why. I agree junit reporter is not the right place to fix, but am not sure I can track it down in karma. It's fine if you just decline this PR

[eggers]

This is an annoying bug for us. Can we get this merged in if it does fix the problem, even if the root problem is in karma?

[j0tunn]

Any progress on this PR? I think it should be merged: no matter what caused the problem, the problem is here

[dignifiedquire]

Fixed in karma.