Address Coverity issue: filelength() can return negative value

src/sbbs3/getnode.cpp

-/* getnode.cpp */
-
 /* Synchronet node information retrieval functions */
 
-/* $Id: getnode.cpp,v 1.56 2020/08/01 22:04:03 rswindell Exp $ */
-
 /****************************************************************************
  * @format.tab-size 4		(Plain Text/Source Code File Header)			*
  * @format.use-tabs true	(see http://www.synchro.net/ptsc_hdr.html)		*
@@ -17,21 +13,9 @@
  * See the GNU General Public License for more details: gpl.txt or			*
  * http://www.fsf.org/copyleft/gpl.html										*
  *																			*
- * Anonymous FTP access to the most recent released source is available at	*
- * ftp://vert.synchro.net, ftp://cvs.synchro.net and ftp://ftp.synchro.net	*
- *																			*
- * Anonymous CVS access to the development source and modification history	*
- * is available at cvs.synchro.net:/cvsroot/sbbs, example:					*
- * cvs -d :pserver:anonymous@cvs.synchro.net:/cvsroot/sbbs login			*
- *     (just hit return, no password is necessary)							*
- * cvs -d :pserver:anonymous@cvs.synchro.net:/cvsroot/sbbs checkout src		*
- *																			*
  * For Synchronet coding style and modification guidelines, see				*
  * http://www.synchro.net/source.html										*
  *																			*
- * You are encouraged to submit any modifications (preferably in Unix diff	*
- * format) via e-mail to mods@synchro.net									*
- *																			*
  * Note: If this box doesn't appear square, then you need to fix your tabs.	*
  ****************************************************************************/
 
@@ -257,7 +241,7 @@ int sbbs_t::getnmsg(bool clearline)
 		return(errno); 
 	}
 	length=(long)filelength(file);
-	if(!length) {
+	if(length <= 0) {
 		close(file);
 		return(0); 
 	}

src/sbbs3/str.cpp

@@ -457,7 +457,7 @@ void sbbs_t::read_sif_dat(char *siffile, char *datfile)
 		return; 
 	}
 	length=(long)filelength(file);
-	if(!length) {
+	if(length <= 0) {
 		close(file);
 		return; 
 	}