ioc/dbStatic: make offset in field description an unsigned short, add cast to code generator

fixes ~2600 compiler warnings (on windows-x64)

src/ioc/dbStatic/dbBase.h

@@ -88,7 +88,7 @@ typedef struct dbFldDes{  /* field description */
     /*On no runtime following only set for STRING			*/
     short	size;		/*length in bytes of a field element	*/
     /*The following are only available on run time system*/
-    short	offset;		/*Offset in bytes from beginning of record*/
+    unsigned short	offset;		/*Offset in bytes from beginning of record*/
 }dbFldDes;
 
 typedef struct dbInfoNode {	/*non-field per-record information*/

src/tools/dbdToRecordtypeH.pl

@@ -124,8 +124,8 @@ sub oldtables {
                 "sizeof(prec->" . $_->C_name . ");"
             } $rtyp->fields) . "\n" .
         join("\n", map {
-                "    prt->papFldDes[${rn}Record" . $_->name . "]->offset = " .
-                "(char *)&prec->" . $_->C_name . " - (char *)prec;"
+                "    prt->papFldDes[${rn}Record" . $_->name . "]->offset = (unsigned short)(" .
+                "(char *)&prec->" . $_->C_name . " - (char *)prec);"
             } $rtyp->fields) . "\n" .
         "    prt->rec_size = sizeof(*prec);\n" .
         "    return 0;\n" .