stagefright aacenc: Avoid a division by zero

In rare cases, the result of normFactor * (*psfbNActiveLines)
could be zero, leading to a division by zero in pow2_xy.

In these cases, normFactor was INT_MIN, and if *psfbNActiveLines
was 2, the product was zero.

normFactor being INT_MIN is a bug in itself though.

Change-Id: Ib31bf02889615a7be3bd1bc028da8a7651a8dbee

media/libstagefright/codecs/aacenc/src/adj_thr.c

@@ -465,7 +465,7 @@ static void correctThresh(PSY_OUT_CHANNEL  psyOutChannel[MAX_CHANNELS],
         deltaSfbPe = *psfbPeFactors * deltaPe;
 
 		/* thr3(n) = thr2(n)*2^deltaSfbPe/b(n) */
-        if (*psfbNActiveLines > 0) {
+        if (*psfbNActiveLines > 0 && (normFactor* (*psfbNActiveLines)) != 0) {
           /* new threshold */
           Word32 thrFactor;
           sfbEn  = psyOutChan->sfbEnergy[sfbGrp+sfb];