Fix misc Coverity defects in camdd(8)

[asomers]

Summary

Fix misc Coverity defects in camdd(8)

CID 1341620 Fix a small memory leak
CID 1341630 Though this is technically a false positive, rearrange the

		code for clarity.

CID 1341635 Eliminate dead code
CID 1368663 Fix a double mutex unlock in the error path

Also:

• Use sig_atomic_t for variables accessed from signal handlers
• Don't conditionalize free(3) on its argument being non-null

Test Plan

Ken, can you please test it? I'm not sure how to test it to get full coverage.

[ken]

Okay, I tested most of the paths affected in the patch and things look good.