webdav: fail soft on time parsing errors

The time format provided by webdav servers seems to vary wildly from
that specified in the RFC - rclone already parses times in 5 different
formats!

If an unparseable time is found, then fail softly logging an ERROR
(just once) but returning the epoch.

This will mean that webdav servers with bad time formats will still be
usable by rclone.

backend/webdav/api/types.go

@@ -6,7 +6,10 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
+
+	"github.com/ncw/rclone/fs"
 )
 
 const (
@@ -148,6 +151,8 @@ var timeFormats = []string{
 	time.RFC3339,   // Wed, 31 Oct 2018 13:57:11 CET (as used by komfortcloud.de)
 }
 
+var oneTimeError sync.Once
+
 // UnmarshalXML turns XML into a Time
 func (t *Time) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
 	var v string
@@ -171,5 +176,14 @@ func (t *Time) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
 			break
 		}
 	}
+	if err != nil {
+		oneTimeError.Do(func() {
+			fs.Errorf(nil, "Failed to parse time %q - using the epoch", v)
+		})
+		// Return the epoch instead
+		*t = Time(time.Unix(0, 0))
+		// ignore error
+		err = nil
+	}
 	return err
 }