lib/model: Don't stop folder if out of disk space (fixes #2370) (#5099)

This removes the out of disk space check from CheckHealth. The disk space is now
only checked if there are files to pull, in which case pulling those files is
stopped, but everything else (dirs, links, deletes) keeps running -> can recover
disk space through pulling.

lib/config/folderconfiguration.go

@@ -282,8 +282,19 @@ func (l FolderDeviceConfigurationList) Len() int {
 	return len(l)
 }
 
-func (f *FolderConfiguration) CheckFreeSpace() error {
-	return checkFreeSpace(f.MinDiskFree, f.Filesystem())
+func (f *FolderConfiguration) CheckAvailableSpace(req int64) error {
+	fs := f.Filesystem()
+	usage, err := fs.Usage(".")
+	if err != nil {
+		return nil
+	}
+	usage.Free -= req
+	if usage.Free > 0 {
+		if err := checkFreeSpace(f.MinDiskFree, usage); err == nil {
+			return nil
+		}
+	}
+	return fmt.Errorf("insufficient space in %v %v", fs.Type(), fs.URI())
 }
 
 type FolderConfigurationList []FolderConfiguration