Do not force linebreaks when MaxEmptyLinesToKeep is 0.

Previously we would format
 call(

     p);
as
 call(
     p);
with MaxEmptyLinesToKeep == 0.

Now we format it as:
  call(p);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@243429 91177308-0d34-0410-b5e6-96231b3b80d8