[bug] DocView.on_mouse_released() gets called twice

[SwissalpS]

to reproduce:

• clone/checkout master at [38bd9b3] (latest as of this writing)
• build it
• add this plugin:

local DocView = require "core.docview"

local omr = DocView.on_mouse_released
function DocView:on_mouse_released(...)
  print 'on_mouse_released....'
  return omr(self, ...) --true --false --nil
end

local omp = DocView.on_mouse_pressed
function DocView:on_mouse_pressed(...)
  print 'on_mouse_pressed'
  return omp(self, ...)
end

• launch lite from terminal
• see that for every click+release output is one pressed and two released:

on_mouse_pressed
on_mouse_released....
on_mouse_released....

[SwissalpS]

adding debug line here:

lite/data/core/init.lua

Line 338 in 38bd9b3

core.root_view:on_mouse_released(...)

shows that the error is on lua side. Here there is only one signal.