Don't use Identity matrix coefficients with 4:0:0

Chrome doesn't render 4:0:0 with Identity matrix coefficients
correctly. Work around this Chrome issue by using matrix coefficients 6
instead with lossless 4:0:0.

Fix AOMediaCodec#1481.

apps/avifenc.c

@@ -1625,12 +1625,10 @@ int main(int argc, char * argv[])
     image->alphaPremultiplied = premultiplyAlpha;
 
     if ((image->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY) && (input.requestedFormat != AVIF_PIXEL_FORMAT_NONE) &&
-        (input.requestedFormat != AVIF_PIXEL_FORMAT_YUV444) && (input.requestedFormat != AVIF_PIXEL_FORMAT_YUV400)) {
-        // User explicitly asked for non YUV444/YUV400 yuvFormat, while
-        // matrixCoefficients was likely set to
-        // AVIF_MATRIX_COEFFICIENTS_IDENTITY as a side effect of --lossless, and
-        // Identity is only valid with YUV444/YUV400. Set matrixCoefficients
-        // back to the default.
+        (input.requestedFormat != AVIF_PIXEL_FORMAT_YUV444)) {
+        // User explicitly asked for non YUV444 yuvFormat, while matrixCoefficients was likely
+        // set to AVIF_MATRIX_COEFFICIENTS_IDENTITY as a side effect of --lossless,
+        // and Identity is only valid with YUV444. Set matrixCoefficients back to the default.
         image->matrixCoefficients = AVIF_MATRIX_COEFFICIENTS_BT601;
 
         if (cicpExplicitlySet) {
@@ -1663,8 +1661,7 @@ int main(int argc, char * argv[])
     }
 
     // Check again for y4m input (y4m input ignores input.requestedFormat and retains the format in file).
-    if ((image->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY) && (image->yuvFormat != AVIF_PIXEL_FORMAT_YUV444) &&
-        (image->yuvFormat != AVIF_PIXEL_FORMAT_YUV400)) {
+    if ((image->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY) && (image->yuvFormat != AVIF_PIXEL_FORMAT_YUV444)) {
         fprintf(stderr, "matrixCoefficients may not be set to identity (0) when subsampling.\n");
         returnCode = 1;
         goto cleanup;