Rewritten 808x CPU emulation core based on reenigne's XTCE, VisiOn, SnatchIt, and 8088 MPH now work correctly;

Fixed PC speaker sound volume in PIT mode 0;
A few CPU emulation clean-ups;
Hard disk controller changing redone in a less messy way;
Re-added the long-missing key send delay handling to the XT keyboard handler;
Fixed a bug that was causing SLiRP not to work when compiled with MingW/GCC 7.3.0-2 or newer;
Some serial mouse and port fixes;
A lot of changes to printer emulation, mostly based on DOSBox-X;
Printer PNG writer now uses statically linked libpng;
Added support for the HxC MFM floppy image format and upped 86F format version to 2.12;
Ported various things from PCem and some from VARCem;
Added the S3 86c801/805 emulation (patch from TheCollector1995);
Fixed and renamed the EGA monitor options;
Better synchronized the 808x to the PIT and the CGA;
Fixed the CGA wait state calculation;
Cleaned up some things in mem.c;
Fixed some things in the floppy emulation to make VisiOn get the correct errors from the copy protection disk;
Fixed several renderer-related bugs, including the SDL2 renderer's failure to take screenshots;
The Jenkins builds are now compiled with MingW/GCC 7.4.0-1 and include all the required DLL's.

src/cdrom/cdrom_image.cc

@@ -8,7 +8,7 @@
  *
  *		CD-ROM image support.
  *
- * Version:	@(#)cdrom_image.cc	1.0.7	2018/10/28
+ * Version:	@(#)cdrom_image.cc	1.0.9	2019/02/01
  *
  * Author:	RichardG867,
  *		Miran Grca, <mgrca8@gmail.com>
@@ -292,6 +292,6 @@ cdrom_image_close(cdrom_t *dev)
 {
     cdrom_image_log("CDROM: image_close(%ls)\n", dev->image_path);
 
-    if (dev->ops->exit)
+    if (dev && dev->ops && dev->ops->exit)
 	dev->ops->exit(dev);
 }