Make fluidsynth calling ipatch_close()

[jjceresa]

This should address issue #643

Warning: this works only if swami/libinstpatch#47 is applied, otherwise Swami will fail with memory violation.

[derselbst]

Technically, this change would have required bumping the minimum required libinstpatch version. To avoid that, I've made it backward compatible and added the missing call to ipatch_init() into new_fluid_synth().

[jjceresa]

I've made it backward compatible.

Thanks !

[jjceresa]

Just tried current fluidsynth master with current libinspatch and current swami. This works. Thanks.