Make sure backup_writer is set before using its logging

git-svn-id: http://svn.savannah.nongnu.org/svn/rdiff-backup@683 2b77aa54-bcbc-44c9-a7ec-4f6cf2b41109

branches/r1-0/rdiff-backup/rdiff_backup/log.py

@@ -247,7 +247,7 @@ or within one second of each other.  Wait a second and try again.""" %
 
 	def write_if_open(cls, error_type, rp, exc):
 		"""Call cls.write(...) if error log open, only log otherwise"""
-		if not Globals.isbackup_writer:
+		if not Globals.isbackup_writer and Globals.backup_writer:
 			return Globals.backup_writer.log.ErrorLog.write_if_open(
 				error_type, rp, str(exc)) # convert exc bc of exc picking prob
 		if cls.isopen(): cls.write(error_type, rp, exc)