collapsible_if shouldn't warn on `else` after multiple `else if`

[leoyvens]

Consider:

if cond {
  ...
} else if cond1 {
  bar
} else if cond2 {
  ...
} else if cond3 {
  ...
} else {
  bar
}

This will trigger collapsible_if because of two equal bodies containing bar, but collapsing those ifs would be ugly and error prone, the code is idiomatic as it is.

[camsteffen]

Could not reproduce.