Set X11DRV_DeviceCaps.numColors according to doc (fixes Cubase VST24

graphics/x11drv/init.c

@@ -194,6 +194,12 @@ BOOL X11DRV_GDI_Initialize(void)
     X11DRV_DevCaps.vertRes   = screen_height;
     X11DRV_DevCaps.bitsPixel = screen_depth;
 
+    /* MSDN: Number of entries in the device's color table, if the device has
+     * a color depth of no more than 8 bits per pixel.For devices with greater
+     * color depths, -1 is returned.
+     */
+    X11DRV_DevCaps.numColors = (screen_depth>8)?-1:(1<<screen_depth);
+ 
     /* Resolution will be adjusted during the font init */
 
     X11DRV_DevCaps.logPixelsX = (int)(X11DRV_DevCaps.horzRes * 25.4 / X11DRV_DevCaps.horzSize);