subass: Fix crash in the simple SSA/ASS decoder.

This is the issue exploited by the anime groups.
We now skip anything in { }
Note that ass/ssa cannot have a valid string with text { text } text.
(cherry picked from commit f77a6c48)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/subtitles/subsass.c

@@ -93,16 +93,15 @@ void ParseSSAString( decoder_t *p_dec,
             i_text++;
             psz_buffer_sub += 2;
         }
-        else if( psz_buffer_sub[0] == '{' &&
-                 psz_buffer_sub[1] == '\\' )
+        else if( psz_buffer_sub[0] == '{' )
         {
-            /* SSA control code */
+            /* { } Control code in SSA. Cannot be escaped */
             while( psz_buffer_sub[0] != '\0' &&
                    psz_buffer_sub[0] != '}' )
             {
                 psz_buffer_sub++;
             }
-            psz_buffer_sub++;
+            if( psz_buffer_sub[0] == '}' ) psz_buffer_sub++;
         }
         else
         {