Fixing the issue with a command with subcommands not showing help message.

- the command name is "" and HasName was returning true for an empty
  ShortName.
- the Show method wasn't aware that command name was just "" and
  returned the first subcommand.

command.go

@@ -119,7 +119,7 @@ func (c Command) Run(ctx *Context) error {
 
 // Returns true if Command.Name or Command.ShortName matches given name
 func (c Command) HasName(name string) bool {
-	return c.Name == name || c.ShortName == name
+	return c.Name == name || (c.ShortName != "" && c.ShortName == name)
 }
 
 func (c Command) startApp(ctx *Context) error {