Fix a typo in the diagnostic context for 'ipco'

The diagnostic messages in avifParseItemPropertyContainerBox() should
say "Box[ipco]", not "Box[iprp]".

src/read.c

diff --git a/src/read.c b/src/read.c
index 9dc5396..c0bf45a 100644
--- a/src/read.c
+++ b/src/read.c
@@ -1578,7 +1578,7 @@
 
 static avifBool avifParseItemPropertyContainerBox(avifPropertyArray * properties, const uint8_t * raw, size_t rawLen, avifDiagnostics * diag)
 {
-    BEGIN_STREAM(s, raw, rawLen, diag, "Box[iprp]");
+    BEGIN_STREAM(s, raw, rawLen, diag, "Box[ipco]");
 
     while (avifROStreamHasBytesLeft(&s, 1)) {
         avifBoxHeader header;