Fix sized filesystem

If purging is enabled, overwriting a file with a file of the same
or smaller size will not result in an error.

It is now possible to change the purging mode on an existing sized
filesystem.

app/api/api.go

@@ -426,7 +426,7 @@ func (a *api) start() error {
 	} else {
 		a.memfs.SetMetadata("base", baseMemFS.String())
 		if sizedfs, ok := a.memfs.(fs.SizedFilesystem); ok {
-			sizedfs.Resize(cfg.Storage.Memory.Size * 1024 * 1024)
+			sizedfs.Resize(cfg.Storage.Memory.Size*1024*1024, cfg.Storage.Memory.Purge)
 		}
 	}