clang-format: [JS] don't break comments before any '{'

Summary:
Previously, clang-format would avoid breaking before the first `{`
found, but then happily break before subsequent '{'s on the line. This
change fixes that by looking for the first location that has no opening
curly, if any.

This fixes the original commit by correcting the loop condition.

This reverts commit 66dc646e09b795b943668179c33d09da71a3b6bc.

Reviewers: krasimir

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D50249

llvm-svn: 338890