Fixed proxy_redirect off inheritance.

Example configuration to reproduce:

  server {
      proxy_redirect off;

      location / {
          proxy_pass http://localhost:8000;
          proxy_redirect http://localhost:8000/ /;

          location ~ \.php$ {
              proxy_pass http://localhost:8000;
              # proxy_redirect must be inherited from the level above,
              # but instead it was switched off here
          }
      }
  }