decoder/API: move part of decoder_check_cancel_read() into class DecoderBridge

src/decoder/Bridge.hxx

@@ -107,6 +107,15 @@ public:
 
 	~DecoderBridge();
 
+	/**
+	 * Should be read operation be cancelled?  That is the case when the
+	 * player thread has sent a command such as "STOP".
+	 *
+	 * Caller must lock the #DecoderControl object.
+	 */
+	gcc_pure
+	bool CheckCancelRead() const;
+
 	/**
 	 * Returns the current chunk the decoder writes to, or allocates a new
 	 * chunk if there is none.