adapt to current Rack development version, and fix some issues en-passant

[holgerschurig]

Hi,

after I did the adaption to the 0.6.0dev API, I found out by chance that dizzisound also did this. *) So it seems that people want compile your code against the newest-and-hottest (and buggiest, lol) Rack.

While I adapted the plugins, I also noticed some errors from my Linux GCC compiler. And while at it, I thought "Hey, let's throw clang's static analyzer onto the code". And it also found some things. I fixed all of them.

*) https://github.com/dizzisound/VCV-Rack-Plugins/commit/774f6dc59c2a1dca9bfbaea49b946e0b5c9fd78a ... he didn't create a pull request

[dizzisound]

@holgerschurig Hi Holger, only to inform you that I didn't proceeded with a PR as per this issue: https://github.com/mschack/VCV-Rack-Plugins/issues/55 that was then closed by @cschol
In short, the dev wished to make the update himself, so as to upgrade the modules with new features he hadn't pushed yet. Regards

[mschack]

sorry guys, i missed this and submitted my 0.6 build