Use saturating adds to avoid overflow

These additions can overflow, triggering assertions later.

libAACenc/src/aacenc_tns.cpp

@@ -1150,8 +1150,8 @@ static INT FDKaacEnc_AutoToParcor(
     for(j=numOfCoeff-i-1; j>=0; j--) {
       FIXP_DBL accu1 = fMult(tmp, input[j]);
       FIXP_DBL accu2 = fMult(tmp, workBuffer[j]);
-      workBuffer[j] += accu1;
-      input[j] += accu2;
+      workBuffer[j] = fAddSaturate(workBuffer[j], accu1);
+      input[j] = fAddSaturate(input[j], accu2);
     }
 
     workBuffer++;

libAACenc/src/grp_data.cpp

@@ -195,7 +195,7 @@ FDKaacEnc_groupShortData(FIXP_DBL      *mdctSpectrum,     /* in-out
       FIXP_DBL energy = sfbEnergy->Short[wnd][sfb];
       for (j=1; j<groupLen[grp]; j++)
       {
-        energy += sfbEnergy->Short[wnd+j][sfb];
+        energy = fAddSaturate(energy, sfbEnergy->Short[wnd+j][sfb]);
       }
       sfbEnergy->Long[i++] = energy;
     }