Fix overflow in CELT Deep PLC

Added proper saturation and rounding
diff --git a/celt/celt_decoder.c b/celt/celt_decoder.c
index 70b5ed1..743c203 100644
--- a/celt/celt_decoder.c
+++ b/celt/celt_decoder.c
@@ -589,7 +589,7 @@
       for (j=0;j<SINC_ORDER+1;j++) {
          sum += buf48k[3*i + j + offset]*sinc_filter[j];
       }
-      buf16k[i] = sum;
+      buf16k[i] = float2int(MIN32(32767.f, MAX32(-32767.f, sum)));
    }
    tmp_read_post = lpcnet->fec_read_pos;
    tmp_fec_skip = lpcnet->fec_skip;