Effect: change minimum gate to FLT_MIN

This helps reverbs (for example) to not get cut too soon (#424)

(cherry picked from commit f8773b8978f72b24fd15f5486dc85d81ced1d5b5)
RemoteVstPlugin: really close the plugin

(cherry picked from commit d50d376b2a13b6920c8087e9fa4be5472553aaec)