fix pointer conflict cause go panic, php-fpm will crash.

	nginx-error.log will show: [error] 12199#0: *471 recv() failed (104: Connection reset by peer) while reading response header from upstream,
	kitech#8

Signed-off-by: monkey <nangong92t@gmail.com>

phpgo/extension.go

@@ -426,6 +426,7 @@ func on_phpgo_function_callback_p(cbid int, phpthis unsafe.Pointer,
 			panic("wtf")
 		}
 		gothis := gext.objs_p[phpthis]
+		delete(gext.objs_p, phpthis)
 		// argv = append([]reflect.Value{reflect.ValueOf(gothis)}, argv...)
 		argv[0] = reflect.ValueOf(gothis)
 	}