fix: size the lock-file path buffer to the concat buffer (closes #183)

A long log path made the lock-file path overflow the fixed 256-byte n_lock
buffer, tripping the guarded copy and aborting with signal 6. Size n_lock to
the concat-buffer capacity so it holds any path fconcat can produce.

(cherry picked from commit 15144ffd24667712cca2ac0fee96bd355239eff6)

src/htscoremain.c

@@ -2899,7 +2899,9 @@ static int hts_main_internal(int argc, char **argv, httrackp * opt) {
   }
 
   {
-    char n_lock[256];
+    /* Sized to the concat-buffer capacity so it can always hold the lock-file
+       path produced by fconcat(), even with a long log path (issue #183). */
+    char n_lock[OPT_GET_BUFF_SIZE(opt)];
 
     // on peut pas avoir un affichage ET un fichier log
     // ca sera pour la version 2