Use JS_ValueToECMAUint32 for full 32-bit time_t values

Resolves issue with filelist.js trying to pass 4294967295 (-1) to system.datestr() resulting in:
!JavaScript  /sbbs/exec/filelist.js line 13: Error: can't convert t to an integer

src/sbbs3/js_system.c

@@ -370,7 +370,7 @@ static JSBool js_system_set(JSContext *cx, JSObject *obj, jsid id, JSBool strict
 #ifndef JSDOOR
 	switch(tiny) {
 		case SYS_PROP_MISC:
-			JS_ValueToInt32(cx, *vp, &sys->cfg->sys_misc);
+			JS_ValueToECMAUint32(cx, *vp, &sys->cfg->sys_misc);
 			break;
 		case SYS_PROP_OP_AVAIL:
 			if(!set_sysop_availability(sys->cfg, JSVAL_TO_BOOLEAN(*vp))) {
@@ -1168,7 +1168,7 @@ js_datestr(JSContext *cx, uintN argc, jsval *arglist)
 			JS_SET_RVAL(cx, arglist, DOUBLE_TO_JSVAL((double)dstrtounix(sys->cfg, p)));
 			return(JS_TRUE);
 		}
-		JS_ValueToInt32(cx,argv[0],&t);
+		JS_ValueToECMAUint32(cx,argv[0],&t);
 	}
 	unixtodstr(sys->cfg,t,str);
 	if((js_str = JS_NewStringCopyZ(cx, str))==NULL)
@@ -1183,7 +1183,7 @@ js_secondstr(JSContext *cx, uintN argc, jsval *arglist)
 {
 	jsval *argv=JS_ARGV(cx, arglist);
 	char		str[128];
-	int32		t=0;
+	uint32_t	t=0;
 	JSString*	js_str;
 
 	JS_SET_RVAL(cx, arglist, JSVAL_NULL);
@@ -1195,7 +1195,7 @@ js_secondstr(JSContext *cx, uintN argc, jsval *arglist)
 		JS_ReportError(cx, "Invalid argument");
 		return JS_FALSE;
 	}
-	JS_ValueToInt32(cx,argv[0],&t);
+	JS_ValueToECMAUint32(cx,argv[0],&t);
 	sectostr(t,str);
 	if((js_str = JS_NewStringCopyZ(cx, str))==NULL)
 		return(JS_FALSE);