mp3dec: Zero initialize decoder memory during initialization

Bug: 144901522
Test: poc in bug
Test: atest android.mediav2.cts
Test: atest atest android.media.cts.DecoderTest

Change-Id: I28e49f7b07392cd74a8cfeb90e106e6b762504c5

media/libstagefright/codecs/mp3dec/src/pvmp3_framedecoder.cpp

@@ -659,20 +659,12 @@ void pvmp3_InitDecoder(tPVMP3DecoderExternal *pExt,
     huffcodetab       *pHuff;
 
     pVars = (tmp3dec_file *)pMem;
-
-    pVars->num_channels = 0;
+    memset(pVars, 0, sizeof(*pVars));
 
     pExt->totalNumberOfBitsUsed = 0;
     pExt->inputBufferCurrentLength = 0;
     pExt->inputBufferUsedLength    = 0;
 
-    pVars->mainDataStream.offset = 0;
-
-    pv_memset((void*)pVars->mainDataBuffer,
-              0,
-              BUFSIZE*sizeof(*pVars->mainDataBuffer));
-
-
     pVars->inputStream.pBuffer = pExt->pInputBuffer;
 
     /*