Fix clang-format's expression parser for leading }s.

The leading "}" in the construct "} else if (..) {" was confusing the
expression parser. Thus, no fake parentheses were generated and the
indentation was broken in some cases.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183393 91177308-0d34-0410-b5e6-96231b3b80d8