Statically assert a strcpy is safe

src/read.c

diff --git a/src/read.c b/src/read.c
index a768ed9..8592275 100644
--- a/src/read.c
+++ b/src/read.c
@@ -4524,6 +4524,7 @@
         colorItem->premByID = alphaIsPremultiplied;
         avifProperty * alphaAuxProp = avifMetaCreateProperty(meta, "auxC");
         AVIF_CHECKERR(alphaAuxProp, AVIF_RESULT_OUT_OF_MEMORY);
+        static_assert(sizeof(alphaAuxProp->u.auxC.auxType) >= sizeof(AVIF_URN_ALPHA0), "");
         strcpy(alphaAuxProp->u.auxC.auxType, AVIF_URN_ALPHA0);
         AVIF_CHECKERR(avifDecoderItemAddProperty(alphaItem, alphaAuxProp), AVIF_RESULT_OUT_OF_MEMORY);