Use Tokens::ensureWhitespaceAtIndex to simplify code

[kubawerlos]

It lowers cyclomatic complexity.

Before:

$ phploc src/Fixer | grep 'Average Complexity per Class'
  Average Complexity per Class                   17.27

After:

$ phploc src/Fixer | grep 'Average Complexity per Class'
  Average Complexity per Class                   17.22

[coveralls]

Coverage increased (+0.001%) to 92.854% when pulling 867da40 on werlos:use_Tokens_ensureWhitespaceAtIndex into 07430f5 on FriendsOfPHP:master.

[SpacePossum]

Thank you @kubawerlos.