Only count assembly for size when no size present

[samfriedman]

Counting assembly bytes doesn't work properly for constant data in the .text section, which causes underreporting of sizes. The actual size reported by nm is present and accurate, so we prefer that and only count assembly bytes when nm doesn't give us a size.

[HBehrens]

This is absolutely the right thing to do, thank you @samfriedman ! Unfortunately, this change won't merge cleanly anymore. Unless you are volunteering to do so, I will rebase your change on top of master and write a test for it to prevent future regressions before merging it.