vcd: fix NULL dereference on error

(cherry picked from commit a1c81a10276b3839c9832d274ae5def3c53ee203)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/access/vcd/cdrom.c

@@ -782,30 +782,33 @@ static int OpenVCDImage( vlc_object_t * p_this, const char *psz_dev,
     {
         /* psz_dev must be the cue file. Let's assume there's a .bin
          * file with the same filename */
-        psz_vcdfile = malloc( p_pos - psz_dev + 5 /* ".bin" */ );
-        strncpy( psz_vcdfile, psz_dev, p_pos - psz_dev );
-        strcpy( psz_vcdfile + (p_pos - psz_dev), ".bin");
+        if( asprintf( &psz_vcdfile, "%.*s.bin", (int)(p_pos - psz_dev),
+                      psz_dev ) < 0 )
+            psz_vcdfile = NULL;
         psz_cuefile = strdup( psz_dev );
     }
     else
+    if( p_pos )
     {
         /* psz_dev must be the actual vcd file. Let's assume there's a .cue
          * file with the same filename */
-        if( p_pos )
-        {
-            psz_cuefile = malloc( p_pos - psz_dev + 5 /* ".cue" */ );
-            strncpy( psz_cuefile, psz_dev, p_pos - psz_dev );
-            strcpy( psz_cuefile + (p_pos - psz_dev), ".cue");
+        if( asprintf( &psz_cuefile, "%.*s.cue", (int)(p_pos - psz_dev),
+                      psz_dev ) < 0 )
+            psz_cuefile = NULL;
+        psz_vcdfile = strdup( psz_dev );
     }
     else
     {
         if( asprintf( &psz_cuefile, "%s.cue", psz_dev ) == -1 )
             psz_cuefile = NULL;
-        }
-        /* If we need to look up the .cue file, then we don't have to look for the vcd */
+         /* If we need to look up the .cue file, then we don't have to look
+          * for the vcd */
         psz_vcdfile = strdup( psz_dev );
     }
 
+    if( psz_cuefile == NULL || psz_vcdfile == NULL )
+        goto error;
+
     /* Open the cue file and try to parse it */
     msg_Dbg( p_this,"trying .cue file: %s", psz_cuefile );
     cuefile = vlc_fopen( psz_cuefile, "rt" );