Fix inconsistent code styles in OkHttpStreamFetcher.

[floating-cat]

No description provided.

[coveralls]

Coverage remained the same at 84.06% when pulling 4eba230 on floating-cat:master into c78ee4e on bumptech:master.

[sjudd]

Thanks!

[TWiStErRob]

Thanks for the PR!

Some (late) feedback: In general I prefer putting the if outside the try, because entering/exiting try may be slower.

Even though I didn't find any hard evidence on this in the last 10 minutes of research, this statement is convinced me to continue preferring it:

Placing code inside a try-catch block inhibits certain optimizations that modern JVM implementations might otherwise perform.

It also helps devs to skip the try block if they're reading code and they know a certain variable's nullity.

[sjudd]

Makes sense, when we pull this stuff into a utility method (more pull requests always welcome :)), we can if outside of try.