libtt: Further coverity fixes

cde/lib/tt/bin/ttdbserverd/dm_server.C

@@ -1561,7 +1561,10 @@ _tt_transaction_1(_Tt_transaction_args* args, SVCXPRT * /* transp */)
 			return _tt_transaction_error(fd);
 		}
 		/* Turn on close-on-exec */
-		fcntl(fd, F_SETFD, 1);
+		if(fcntl(fd, F_SETFD, 1) == -1) {
+			res.iserrno = DM_WRITE_FAILED;
+			return _tt_transaction_error(fd);
+		}
 
 		/* reset to beginning of file */
 		off_t offset;

cde/lib/tt/bin/ttsession/mp_server.C

@@ -251,12 +251,12 @@ int main(int argc, char **argv)
 				_tt_syslog( errstr, LOG_ERR, "%m" );
 				exit(1);
 			}
-			cargv[i] = '\0';
+			cargv[i] = NULL;
 
 			// if no program given then use $SHELL
 			if (! cargv[0]) {
 				cargv[0] = getenv("SHELL");
-				cargv[1] = '\0';
+				cargv[1] = NULL;
 			}
 			cmd = cargv[0];
 			background_mode = 0;