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wav: check for block align overflow [bug #279]

The block align value depends on the encoding and number of channels.
Do the calculation in 32 bits, then check for 16-bit overflow.

--- a/src/wav.c

+++ b/src/wav.c

@@ -1362,7 +1362,7 @@

     uint16_t wChannels;           /* number of channels */

     uint32_t dwSamplesPerSecond;  /* samples per second per channel*/

     uint32_t dwAvgBytesPerSec=0;  /* estimate of bytes per second needed */

-    uint16_t wBlockAlign=0;       /* byte alignment of a basic sample block */

+    uint32_t wBlockAlign=0;       /* byte alignment of a basic sample block */

     uint16_t wBitsPerSample=0;    /* bits per sample */

     /* fmt chunk extension (not PCM) */

     uint16_t wExtSize=0;          /* extra bytes in the format extension */

@@ -1457,6 +1457,13 @@

         default:

                 break;

     }

+

+    if (wBlockAlign > UINT16_MAX) {

+        lsx_fail_errno(ft, SOX_EOF, "Too many channels (%u)",

+                       ft->signal.channels);

+        return SOX_EOF;

+    }

+

     wav->formatTag = wFormatTag;

     wav->blockAlign = wBlockAlign;

     wav->samplesPerBlock = wSamplesPerBlock;