Avoid accessing uninitialised memory in net_crypto.

[iphydf]

On x86 and x86_64, this change has no effect. On IA64, this fixes a
potential hardware exception. A function returned a partially initialised
value of aggregate type. The only caller of this function checks that the
value is valid before accessing it by testing the one definitely
initialised member. Therefore on x86 and derived architectures, there is
no uninitialised memory access. On IA64, with the regular calling
convention, the struct is allocated on the caller stack and passed as a
pointer, so there the uninitialised memory is also never accessed.
However, on calling conventions where one or more struct members past the
first byte are passed in registers or copied in memory, this call can
cause undefined behaviour.

Specifically, the value can contain a trap representation of the integers
(at the very least the 16 bit port) and cause a hardware exception and
SIGFPE in userland.

Regardless of the explanation above, this change fixes an instance of
undefined behaviour that just happened to be OK on all systems we tested
on.

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This change is 

[GrayHatter]

I thought about reviewing the entire calling stack to make sure this is okay. But instead, I'm just going to accept it because it's an obviously better fix.

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Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[nurupo]

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Comments from Reviewable