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.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
end_of_line = lf
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
end_of_line = lf
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false
end_of_line = lf