matchers: use correct method for finding index in vector
The path matcher has an optimization for when all paths are `rootfilesin:`. This
optimization exists in both Python and Rust. However, the Rust implementation
currently has a bug that makes it fail in most cases. The bug is that it
`rfind()` where it was clearly intended to use `rposition()`. This patch fixes
that and adds a test.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}