[clang-tidy] readability-misleading-indentation: fix chained if

Summary:
Fixed erroneously flagging of chained if statements when styled like this:

```
if (cond) {
}
else if (cond) {
}
else {
}
```

Reviewers: xazax.hun, alexfh

Reviewed By: xazax.hun, alexfh

Subscribers: JDevlieghere, cfe-commits

Patch by Florian Gross!

Differential Revision: https://reviews.llvm.org/D30841

llvm-svn: 298059