Fix counted channel counter after await

ktor-io/common/src/io/ktor/utils/io/CountedByteReadChannel.kt

@@ -36,8 +36,7 @@ public class CountedByteReadChannel(public val delegate: ByteReadChannel) : Byte
     override suspend fun awaitContent(): Boolean {
         val before = delegate.availableForRead
         val result = delegate.awaitContent()
-        val after = delegate.availableForRead
-        count += (before - after).toLong()
+        count += (initial - before).toLong()
         initial = delegate.availableForRead
         return result
     }