fix off by one error

BLRG-PT-18-004

Change-Id: I9cd2582aebf2b33d40f23254047c35c8dee90f4b
Reviewed-on: https://gerrit.libreoffice.org/63508Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

onlineupdate/source/libmar/sign/nss_secutil.c

@@ -122,7 +122,7 @@ SECU_FilePasswd(PK11SlotInfo *slot, PRBool retry, void *arg)
     return 0;  /* no good retrying - the files contents will be the same */
   }
 
-  phrases = PORT_ZAlloc(maxPwdFileSize);
+  phrases = PORT_ZAlloc(maxPwdFileSize + 1);
 
   if (!phrases) {
     return 0; /* out of memory */