Is your feature request related to a problem? Please describe.
I was trying to import bookmarks from a Google Maps Takeout export, with a .kml file generated by a script in order to tweak the metadata slightly. Trying to import it into Organic Maps would tell me "1 file was found. You can see it after conversion." but then nothing else happened. I had to dig into the logcat and scroll past the imported file (which is dumped in its entirety into the log!) to find an XML parse error further up reported by the parser, presumably meaning the conversion quietly failed.

Describe the solution you would like
If an import fails (for syntax reasons or otherwise), this should alert the user in some way -- possibilities include a notification if we expect the import to take a while on some devices, or a dismissable item in the Lists list where the successful would have appeared.

Describe alternatives you have considered
It could also be a second toast, but this would be less obvious given the file-found toast stays for a few seconds and would then transition to the failed message.