Fix few uninitialized variables and a stack smash in AVI dumper

- Fix uninitialized closed flag in avi_worker
- Fix uninitialized stream parameters in avi_writer
- Fix stack smash in AVI write_pkt (the padding is only 2 bytes, don't
  write an u32 into it!)

src/video/avi.cpp

@@ -187,6 +187,7 @@ namespace
 		ivcodec = info.vcodec;
 		segframes = 0;
 		max_segframes = info.max_frames;
+		closed = false;
 		fire();
 	}
 

src/video/avi/codec.cpp

@@ -56,7 +56,7 @@ namespace
 		char buf[8 + PADGRANULARITY];
 		serialization::u32l(buf + 0, fulltype);
 		serialization::u32l(buf + 4, pkt.payload.size());
-		serialization::u32l(buf + 8, 0);
+		serialization::u16l(buf + 8, 0);
 		size_t padding = (PADGRANULARITY - pkt.payload.size() % PADGRANULARITY) % PADGRANULARITY;
 		avifile.outstream->write(buf, 8);
 		avifile.outstream->write(&pkt.payload[0], pkt.payload.size());

src/video/avi/writer.cpp

@@ -97,4 +97,5 @@ avi_writer::avi_writer(const std::string& _prefix, struct avi_video_codec& _vcod
 	next_segment = 0;
 	samplerate = _samplerate;
 	channels = _audiochannels;
+	curwidth = curheight = curfps_n = curfps_d = 0;
 }