Fix `EnsureSingleSpaceAfterTokenChecker` when token is first one on line.

In this case the token's "associated whitespace" contains a newline. If checking for space _before_ token, then this means the check can be skipped - no need to check for a space before if there is a newline before. The bug is when the check is for space _after_: in this case we do _not_ want to skip the check - having a newline before does not mean we don't want a space after!
Merge pull request #119 from bensymonds/fix-ensure-space-after

Fix `EnsureSingleSpaceAfterTokenChecker` when token is first one on line.