FileTarget stuck if no log is found on startup

[rsteneteg]

Describe the bug
A fix that was made to prevent Promtail to stop reading logs from recreated statefulset pods (#3586), it had an unexpected side effect that if a FileTarget don't find any logs at startup it will be stuck and not detect them if they later get created.

To Reproduce
Steps to reproduce the behavior:

1. Start Promtail with a file target to a path that don't have any matching logs.
2. After Promtail as started, create a log file in the watched filetarget path

Expected behavior
Once a matching logfile is created Promtail should automatically detect it and start tailing it.

Screenshots, Promtail config, or terminal output
Scrape job

        static_configs:
          - targets:
              - localhost
            labels:
              __path__: "/foobar/*.log"

[Zeezee1210]

Hey, same issue here.