xerr/Errorv: Don't forget to handle empty-vector case in Error()

Previously Error() was giving "0 errors", but "" seems to be a better
choice.

Anyway proper usage of Errorv is to call .Err() when handing result to
some where so this way empty-vector case becomes nil.

xerr/xerr.go

@@ -21,7 +21,10 @@ import (
 type Errorv []error
 
 func (errv Errorv) Error() string {
-	if len(errv) == 1 {
+	switch len(errv) {
+	case 0:
+		return ""
+	case 1:
 		return errv[0].Error()
 	}
 

xerr/xerr_test.go

@@ -32,6 +32,8 @@ func TestErrorv(t *testing.T) {
 		}
 	}
 
+	check(nil, "")
+
 	err1 := errors.New("err1")
 	err2 := errors.New("err2")