[clang-format] Fix SpacesInSquareBrackets for Lambdas with Initial "&ref" Parameter

Summary:
This fixes an edge case in the `SpacesInSquareBrackets` option where an initial `&ref` lambda parameter is not padded with an initial space.

`int foo = [&bar ]() {}` is fixed to give `int foo = [ &bar ]() {}`

Reviewers: MyDeveloperDay, klimek, sammccall

Reviewed by: MyDeveloperDay

Subscribers: cfe-commits

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D69649