Get rid of unpleasant cast, it causes SIGSEGV

Having a difficult choice between unplasant
cast to get a void * into an enumeration type
and "Something's wrong here" double cast
I decided for the latter.

At least it does not crash when the legal
value of zero is passed as the argument.

cde/programs/dtmail/dtmail/DmxPrintOptions.C

@@ -672,11 +672,8 @@ DmxPrintOptions::isValidMarginSpec(PropUiItem* pui, void* data)
     char	*marginSpec = NULL;
     XtEnum	parseError;
     Widget	text;
-#if defined(linux) || defined(CSRG_BASED)
+
-    _DtPrintMarginEnum which = *((_DtPrintMarginEnum *) data);
+    _DtPrintMarginEnum which = (_DtPrintMarginEnum)(long)data;
-#else
-    _DtPrintMarginEnum which = (_DtPrintMarginEnum) data;
-#endif
 
     text = pui->getWidget();
     if (text)