reproducible hang

[mrRay]

i found a reproducible hang!

dependencies:

• please grab the latest test server from the slack (0.4.2.3), it includes a build of commit 648c86cf6692213a56415cb822572d0b37e14b73 from oscqueryhtml. you may want to delete the sample document (~/Documents/OSCQuery Server/SampleDocument.json) and let this app re-install a fresh copy, but this may not be necessary- i'm just trying to make sure that when you open this doc you have a /test/my_2DPos OSC method.
• please grab the latest release build of the browser (0.4.2.2) from the repos (https://github.com/Vidvox/VVOSCQueryProtocol/releases).

steps to reproduce:

• launch the test server, open the default file (~/Documents/OSCQuery Server/SampleDocument.json)
• click on the URL in the test server that displays the HTML UI in your browser of choice. i'm using chrome, but i've confirmed that the hang is reproducible with safari, too.
• enable bidirectional streaming in the HTML UI
• launch the native browser app, make sure you're viewing the test server.
• locate the sliders for /test/my_2Dpos. click and drag on one of them rapidly, while observing the test server's window- which displays received OSC messages- in the background. the test server should continue receiving values even after you let go of the mouse, and quit the native browser.
• the html page is unresponsive, and must be closed. as soon as it's closed, everything's fine- the test server continues functioning as normal (you can open a new html page and it works as expected). it kind of feels like the html UI is getting stuck in a loop when the test server echoes the value back to it, but that's just a very subjective impression.

another note:

• i've also managed to reproduce this bug without the native cocoa app. clicking & dragging rapidly on the same slider in the html UI can provoke this behavior (while bidirectional streaming is enabled!), but it wasn't as immediately reproducible as it was when using the native cocoa app, so that's what i wrote the report against.
• sample video: https://www.vidvox.net/rays_oddsnends/18.08.27-Main%20Output-13.05.55.mov

[dustmop]

Easily reproduced this bug. Am trying the same fix that was used for the color control, counting the number of outgoing OSC messages and waiting to receive echos in order to avoid loop. Implemented by 0ba0c2f.