Fallback to system font if Wimp$Font is unset

If the configured desktop font is 0 (use Wimp$Font) but that variable is unset, use system font instead like the Wimp does rather than failing to get a font handle from Font Manager.
Refactor the extraction of configured font from CMOS using bitshift and mask future tech.

Version 2.04. Tagged as 'Chars-2_04'

VersionASM

@@ -11,13 +11,13 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "2.03"
-Module_Version          SETA    203
+Module_MajorVersion     SETS    "2.04"
+Module_Version          SETA    204
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "12 Aug 2017"
-Module_ApplicationDate  SETS    "12-Aug-17"
+Module_Date             SETS    "13 Apr 2018"
+Module_ApplicationDate  SETS    "13-Apr-18"
 Module_ComponentName    SETS    "Chars"
 Module_ComponentPath    SETS    "castle/RiscOS/Sources/Apps/Chars"
-Module_FullVersion      SETS    "2.03"
-Module_HelpVersion      SETS    "2.03 (12 Aug 2017)"
+Module_FullVersion      SETS    "2.04"
+Module_HelpVersion      SETS    "2.04 (13 Apr 2018)"
                         END

VersionNum

-/* (2.03)
+/* (2.04)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        2.03
+#define Module_MajorVersion_CMHG        2.04
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                12 Aug 2017
+#define Module_Date_CMHG                13 Apr 2018
 
-#define Module_MajorVersion             "2.03"
-#define Module_Version                  203
+#define Module_MajorVersion             "2.04"
+#define Module_Version                  204
 #define Module_MinorVersion             ""
-#define Module_Date                     "12 Aug 2017"
+#define Module_Date                     "13 Apr 2018"
 
-#define Module_ApplicationDate          "12-Aug-17"
+#define Module_ApplicationDate          "13-Apr-18"
 
 #define Module_ComponentName            "Chars"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Apps/Chars"
 
-#define Module_FullVersion              "2.03"
-#define Module_HelpVersion              "2.03 (12 Aug 2017)"
-#define Module_LibraryVersionInfo       "2:3"
+#define Module_FullVersion              "2.04"
+#define Module_HelpVersion              "2.04 (13 Apr 2018)"
+#define Module_LibraryVersionInfo       "2:4"

bas/!RunImage

@@ -202,16 +202,13 @@ SYS "XOS_GenerateError",Block% TO a$
 
 DEF FNchars_getdesktopfont
 REM Returns a handle and name for the Desktop font
-LOCAL len%,i%,bit%,data%,dfhandle%,df$
-dfhandle%=0
+LOCAL len%,flags%,data%,dfhandle%,df$
 SYS "OS_Byte",161,140 TO ,,data%
-FOR i%=0 TO 3
- IF (data% AND (1<<i%+1)) THEN bit%=1 ELSE bit%=0
- dfhandle%=dfhandle%+(bit%*(2^i%))
-NEXT i%
+dfhandle%=(data% AND&1E)>>1:REM Extract WimpFont configuration bits
 CASE dfhandle% OF
  WHEN 0:
-  SYS "OS_ReadVarVal","Wimp$Font",Block%,255,0,3 TO ,,len%
+  SYS "XOS_ReadVarVal","Wimp$Font",Block%,255,0,3 TO ,,len%;flags%
+  IF(flags% AND1)=1 THEN=FNmsg_get("DF1"):REM Fall back to system font 
   Block%?len%=13:df$=$Block%
  WHEN 1,2,3,4,5,6,7,8,9,10,11,12,13,14:
   df$=FNmsg_get("DF"+STR$dfhandle%)