Last commit to exec.c causes BSOD installing WinXP on i386-softmmu

The last commit to exec.c (360e607b88a23d378f6efaa769c76d26f538234d), causes a BSOD when trying to install a 32bit Windows XP SP-3 image using the pure emulation version of i386-softmmu. A checkout of the previous version of the file (commited in 0169c511554cb0014a00290b0d3d26c31a49818f) solves the problem. Nevertheless, this last commit was intented to solve a BSOD when Xen was used as a hypervisor.