Fix a segfault in IFP's GetUserAttr

[jhrozek]

This PR fixes a crash in GetUserAttr. To reproduce, it's enough to:
dbus-send --print-reply --system --dest=org.freedesktop.sssd.infopipe /org/freedesktop/sssd/infopipe org.freedesktop.sssd.infopipe.GetUserAttr string:admin array:string:name

[fidencio]

Ack!

[lslebodn]

Do you know when the regression was created?
Was it caused by cache-req refactoring?

[fidencio]

@lslebodn,

The issue was introduced by the commit b206e1abb7f6ea373d12537b3338552aed6b656d.
So, yes, it was introduced by the cache-req refactoring.

[lslebodn]

On (16/01/17 01:05), fidencio wrote: @lslebodn, The issue was introduced by the commit [b206e1a] So, yes, it was introduced by the cache-req refactoring.

master: * 9e74a7c LS