[iOS] weex引用原生本地自定义字体文件频繁打印error信息

[demoker]

iOS原生与Weex页面使用同一种字体，会导致一些Weex Error打印, 猜测原因是：原生plist中会先注册一边，然后weex界面加载的时候会根据DomModule中原生提供的字体本地沙盒路径再次进行注册，字体显示是正常的，只是控制台会频繁打印error信息，影响性能

对于原生已经注册的字体，weex SDK里面应该作出相应的判断处理

Log info:
[error]WXUtility.m:568, Unable to register font, but will unregister previous one and retry with new font file, {
src = "file:///private/var/containers/Bundle/Application/E62577F7-C573-414A-89BE-513D9F017BAB/%E7%95%85%E5%90%AC%E6%9E%81%E9%80%9F%E7%89%88.app/Akrobat_kw_Regular.ttf";
localSrc = file:///private/var/containers/Bundle/Application/E62577F7-C573-414A-89BE-513D9F017BAB/%E7%95%85%E5%90%AC%E6%9E%81%E9%80%9F%E7%89%88.app/Akrobat_kw_Regular.ttf;
}.

[error]WXUtility.m:573, We cannot register the font finally. Error Domain=com.apple.CoreText.CTFontManagerErrorDomain Code=105 "Could not register the CGFont '<CGFont (0x280dff680): Akrobat-kw>'" UserInfo={NSDescription=Could not register the CGFont '<CGFont (0x280dff680): Akrobat-kw>', CTFailedCGFont=<CGFont (0x280dff680): Akrobat-kw>}