Don't remove folders when listing throws errors

We're seeing a bug where under certain conditions like a flaky internet
connection, Geary will decide you don't have any remote folders and
simply remove them all locally.  What's probably happening is we're
getting an error and ignoring it.  Since we don't know what the true
error is, this patch simply adds some logging for that case and sets a
flag so we don't run the delete folders logic if there was an error.
Once we get a handle on what's really going on, we can implement a more
surgical fix.

Closes: bgo #726049