avcodec/wma: Fix undefined shift in ff_wma_run_level_decode()

Found-by: Clang -fsanitize=shift
Reported-by: Thierry Foucu <tfoucu@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/wma.c

@@ -451,7 +451,7 @@ int ff_wma_run_level_decode(AVCodecContext *avctx, GetBitContext *gb,
             /** normal code */
             offset                  += run_table[code];
             sign                     = get_bits1(gb) - 1;
-            iptr[offset & coef_mask] = ilvl[code] ^ sign << 31;
+            iptr[offset & coef_mask] = ilvl[code] ^ (sign & 0x80000000);
         } else if (code == 1) {
             /** EOB */
             break;