parser: Fix sigsegv on certain equ instruction parsing
parser: Fix sigsegv on certain equ instruction parsing

We should check for bounds when accessing nasm_reg_flags.
Seems this bug was for long time already.

https://bugzilla.nasm.us/show_bug.cgi?id=3392516

Reported-by: Jordan Zebor <cd687c80a083e27c1fd9d7ee9e312eab6ec2702e@f5.com>
Signed-off-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@gmail.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm