De-obfuscated Poseidon gaschange event building

After some feedback on the mailing list, bitwise XOR wasn't the
preferred way to build the gaschange event.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

file.c

@@ -704,11 +704,11 @@ int parse_txt_file(const char *filename, const char *csv)
 						break;
 					case 85:
 						//He diluent part in %
-						gaschange ^= value << 16;
+						gaschange += value << 16;
 						break;
 					case 86:
 						//O2 diluent part in %
-						gaschange ^= value;
+						gaschange += value;
 						break;
 						//239 Unknown, maybe PO2 at sensor validation?
 						//240 Unknown, maybe PO2 at sensor validation?