"if" in comment can mess up indentaction

[bendk]

• rust.vim version: 4aa69b8

Steps to reproduce:

• Edit a file with "If" inside a comment, on an indented line (I believe "fn" will also trigger the issue)
• Begin and end any block

Expected behavior: The comment shouldn't affect indenting
Actual behavior: The } char will be indented to match the indent of the comment line. Note the leading space in the example below:

/**
 * Something is wrong if rust.vim adds indent to the last line
 */

struct Foo {
 }

I believe this is due to this line, which doesn't take into account if a line is a comment or not: https://github.com/rust-lang/rust.vim/blob/master/indent/rust.vim#L148-L149