Fix a regression introduced by the previous commit

The previous commit confused i_line_count and i_line:
* txt->i_line_count contains the number of text lines.
* txt->i_line is the current offset in txt->line.

As a result no subtitles were available because TextGetLine always returned NULL.
Signed-off-by: Rémi Denis-Courmont <rdenis@simphalempin.com>

modules/demux/vobsub.c

@@ -440,8 +440,8 @@ static int TextLoad( text_t *txt, stream_t *s )
         lines[n++] = psz;
     }
 
-    txt->i_line_count = 0;
-    txt->i_line       = n;
+    txt->i_line_count = n;
+    txt->i_line       = 0;
     txt->line         = lines;
 
     return VLC_SUCCESS;