Fix bug 119085 "cache entries corrupted if size of metadata is zero". sr=darin.

netwerk/cache/src/nsCacheMetaData.cpp

@@ -179,6 +179,8 @@ nsCacheMetaData::FlattenMetaData(char * buffer, PRUint32 bufSize)
 nsresult
 nsCacheMetaData::UnflattenMetaData(char * data, PRUint32 size)
 {
+    if (size == 0)  return NS_OK;
+
     nsresult rv = NS_ERROR_UNEXPECTED;
     char* limit = data + size;
     while (data < limit) {