Fix format error: header chunkSize can be 16, 18, or 40

extras/wav2sketch/wav2sketch.c

 void die(const char *format, ...) __attribute__ ((format (printf, 1, 2)));
 
 // WAV file format:
-// https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
+// http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
 
 const char *filename="";
 char samplename[64];
 	int16_t format, channels, bits;
 	uint32_t rate;
 	uint32_t i, length, padlength=0, arraylen;
+	uint32_t chunkSize;
 	int32_t audio=0;
 
 	// read the WAV file's header
 	for (i=0; i<5; i++) {
 		header[i] = read_uint32(in);
 	}
+	chunkSize = header[4];
 	if (header[0] != 0x46464952 || header[2] != 0x45564157
-	  || header[3] != 0x20746D66 || header[4] != 0x00000010) {
+	  || header[3] != 0x20746D66 || !(chunkSize == 16 || chunkSize == 18 || chunkSize == 40)) {
 		 die("error in format of file %s", filename);
 	}
 
 	if (bits != 16)
 		die("file %s has %d bit format, but only 16 is supported", filename, bits);
 
+	// skip past any extra data on the WAVE header (hopefully it doesn't matter?)
+	for (chunkSize -= 16; chunkSize > 0; chunkSize--) {
+		read_uint8(in);
+	}
+
 	// read the data header, skip non-audio data
 	while (1) {
 		header[0] = read_uint32(in);