Fix Coverity 1498612: integer overflow
Fix Coverity 1498612: integer overflow

The assert added cannot ever fail because (current & 0xFFFF) != 0 from the
while loop and the trailing zero bit count therefore cannot be as large as 32.

Reviewed-by: Tomas Mraz <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@openssl.org>
Reviewed-by: Dmitry Belyavskiy <38c64d6e24766247aad56af3a6ddb0056ad36a44@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/17892)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl