Fix regression where router was overwriting PATH_INFO

On cda64c834bb98a2213f57d57efc40afd6ca527ad `path_info` variable already existed before, so we are overwriting its value.
Add regression test and rename the variable.

[fixes #16926]
[related #17035]

review @rafaelfranca @matthewd @tenderlove 
Use new hash syntax.