[clang-format] Fix a bug causing BeforeLambdaBody to affect brace initialiser formatting

Summary: The condition added with the new setting checked whether the character was an l-brace, not specifically a lambda l-brace, when deciding whether it was possible to break before it or not. This caused the l-brace of some initialiser lists to break onto the next line with the first argument of the initialiser list when the setting was enabled.

Reviewed By: MyDeveloperDay, Wawha

Patch By: duncan-llvm

Subscribers: cfe-commits

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D79022