Some cleanups for https://github.com/fontforge/fontforge/pull/1843 and other

This has some other cleanups to bring down warning message sizes too
OK, I just found this. I thought, when reading it hurriedly above, that you'd found a constant in the czmq headers (even though there's none documented). In fact, you made up a constant. But, in a strange twist, there really is a constant for this in the headers: `ZUUID_LEN`. So use it! I've filed a bug report to the 0MQ developers to ask them to document it.