为什么滤镜链的第一个不能为GPUImageToonFilter？
现象：
滤镜链第一个为GPUImageToonFilter，保存图片或者视频时报错
2021-01-04 22:27:47.662438+0800 为图片添加滤镜水印[8508:2576046] Metal API Validation Enabled 2021-01-04 22:27:51.252910+0800 为图片添加滤镜水印[8508:2576279] *** Assertion failure in -[GPUImageFramebuffer unlock], GPUImageFramebuffer.m:269 2021-01-04 22:27:51.253871+0800 为图片添加滤镜水印[8508:2576279] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Tried to overrelease a framebuffer, did you forget to call -useNextFrameForImageCapture before using -imageFromCurrentFramebuffer?' *** First throw call stack: (0x19eab186c 0x1b3a20c50 0x19e9b7000 0x19fd4b91c 0x10290fe64 0x102945bc4 0x10290ae94 0x102946374 0x1029091e4 0x10290aec0 0x1029091e4 0x10290aec0 0x10294c87c 0x10294d0ec 0x10294db78 0x102a5fbcc 0x102a616c0 0x102a69354 0x102a6a0c0 0x102a76644 0x1ea283804 0x1ea28a75c) libc++abi.dylib: terminating with uncaught exception of type NSException *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Tried to overrelease a framebuffer, did you forget to call -useNextFrameForImageCapture before using -imageFromCurrentFramebuffer?' terminating with uncaught exception of type NSException
