add patch to prevent crash on SCE followed by CPE

hDecoder->element_alloced denotes whether or not we have allocated memory for
usage in terms of the specified channel element. Given that it previously only
had two states (1 meaning allocated, and 0 meaning not allocated), it would not
allocate enough memory for parsing a CPE it if is preceeded by a SCE (and
therefor crash).

These changes fixes the issue by making sure that we allocate additional memory
if so is necessary, and the set of values for hDecoder->element_alloced[n] is
now:

 0 = nothing allocated
 1 = allocated enough for SCE
 2 = allocated enough for CPE

All branches that depend on hDecoder->element_alloced[n] prior to this patch
only checks if the value is, or is not, zero. The added state, 2, is therefor
correctly handled automatically.

https://github.com/videolan/vlc/blob/master/contrib/src/faad2/faad2-fix-cpe-reconstruction.patch

libfaad/specrec.c

@@ -1109,13 +1109,13 @@ uint8_t reconstruct_channel_pair(NeAACDecStruct *hDecoder, ic_stream *ics1, ic_s
 #ifdef PROFILE
     int64_t count = faad_get_ts();
 #endif
-    if (hDecoder->element_alloced[hDecoder->fr_ch_ele] == 0)
+    if (hDecoder->element_alloced[hDecoder->fr_ch_ele] != 2)
     {
         retval = allocate_channel_pair(hDecoder, cpe->channel, (uint8_t)cpe->paired_channel);
         if (retval > 0)
             return retval;
 
-        hDecoder->element_alloced[hDecoder->fr_ch_ele] = 1;
+        hDecoder->element_alloced[hDecoder->fr_ch_ele] = 2;
     }
 
     /* dequantisation and scaling */