Fix a memory leak in bsdinstall

[emaste]

Summary

partedit/part_wizard.c part_wizard
When wizard_parition fails it jumps to the label 'startwizard' which assigns memory to already assigned schemeroot. To fix, move the free of schemeroot.

Test Plan

Use clang's static analyzer, scan-build, to find the problem and later to show resolution.

[emaste]

Handled by 23099099196548550461ba427dcf09dcfb01878d / D40779