Also show help if App/Command Before produces error.

app.go

@@ -164,6 +164,9 @@ func (a *App) Run(arguments []string) (err error) {
 	if a.Before != nil {
 		err := a.Before(context)
 		if err != nil {
+			fmt.Fprintln(a.Writer, err)
+			fmt.Fprintln(a.Writer)
+			ShowAppHelp(context)
 			return err
 		}
 	}

command.go

@@ -149,6 +149,9 @@ func (c Command) Run(ctx *Context) (err error) {
 	if c.Before != nil {
 		err := c.Before(context)
 		if err != nil {
+			fmt.Fprintln(ctx.App.Writer, err)
+			fmt.Fprintln(ctx.App.Writer)
+			ShowCommandHelp(ctx, c.Name)
 			return err
 		}
 	}