Silence a spurious "maybe uninitialized" error.

mlb-rsx.c: In function 'mlb_rsx_entry':
mlb-rsx.c:374:23: warning: 'ent' may be used uninitialized in this function [-Wmaybe-uninitialized]
     fseek(mlb->fp, ent->position, SEEK_SET);
                    ~~~^~~~~~~~~~

It is spurious because ent gets initialized in the loop above.
If the loop is never executed, this must be because 0 >= mlb->nentries
and NULL is returned, so the fseek() is never reached.

mlb-rsx.c

@@ -354,7 +354,7 @@ BUFFER         *mlb_rsx_entry(
     char *name)
 {
     int             i;
-    MLBENT         *ent;
+    MLBENT         *ent = NULL;
     BUFFER         *buf;
     char           *bp;
     int             c;