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]
Merge pull request #17233 from arthurnn/fix_regression_on_path_and_cascade

Fix regression where router was overwriting PATH_INFO