decoder/mpcdec: ignore empty frames

https://bugs.musicpd.org/view.php?id=4656 describes a crash due to division by zero because frame.samples==0. This should never happen, but apparently can happen after seeking. The best we can do is to just ignore this frame.

decoder/mpcdec: ignore empty frames
29a7b2c5 · Max Kellermann · 3b6c285c · 29a7b2c5 · 29a7b2c5
Commit 29a7b2c5 authored Mar 01, 2017 by Max Kellermann
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NEWS NEWS +2 -0

MpcdecDecoderPlugin.cxx src/decoder/plugins/MpcdecDecoderPlugin.cxx +9 -0

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--- a/NEWS
+++ b/NEWS
 ver 0.20.6 (not yet released)
+* decoder
+  - mpcdec: fix crash (division by zero) after seeking

 ver 0.20.5 (2017/02/20)
 * tags

--- a/src/decoder/plugins/MpcdecDecoderPlugin.cxx
+++ b/src/decoder/plugins/MpcdecDecoderPlugin.cxx
@@ -207,6 +207,15 @@ mpcdec_decode(DecoderClient &client, InputStream &is)
 		if (frame.bits == -1)
 			break;

+		if (frame.samples <= 0) {
+			/* empty frame - this has been observed to
+			   happen spuriously after seeking; skip this
+			   obscure frame, and hope libmpcdec
+			   recovers */
+			cmd = client.GetCommand();
+			continue;
+		}
+
 		mpc_uint32_t ret = frame.samples;
 		ret *= info.channels;