When opening a file after micro has started, onBufPaneOpen is not triggered.

Description of the problem or steps to reproduce

When a file is opened (using Ctrl-O) after micro has started, the onBufPaneOpen() method of the plugin is not triggered (while onBufferOpen() method is being triggered as expected).

This is an issue for plugins who wants to provide an "open on start" function and who needs to have access to the pane the buffer is sitting into.

Use the following dummy plugin in ~/.config/micro/plug/dummy/dummy.lua

local micro  = import("micro")

local function pane_str(pane)
    local ret = 'nil'
    if pane then
        ret = pane:ID()..':'..pane.Buf:GetName()
    end
    return ret
end

function onBufferOpen(buf)
    micro.Log('>> onBufferOpen('..buf:GetName()..')')
    micro.Log('<< onBufferOpen')
end

function onBufPaneOpen(pane)
    micro.Log('>> onBufPaneOpen('..pane_str(pane)..')')
    micro.Log('<< onBufPaneOpen')
end

function init()
    micro.Log('>> init')
    micro.Log('<< init')
end

Start micro blank (i.e. no file specified on the command line).
micro -debug

Open a file using Ctrl-O [dummy.lua]
Close the file using Ctrl-Q

The log file will look like this:

2020/03/27 14:06:58 Micro started
2020/03/27 14:07:00 >> onBufferOpen(No name)
2020/03/27 14:07:00 << onBufferOpen
2020/03/27 14:07:00 >> onBufPaneOpen(0:No name)
2020/03/27 14:07:00 << onBufPaneOpen
2020/03/27 14:07:00 >> onBufferOpen(No name)
2020/03/27 14:07:00 << onBufferOpen
2020/03/27 14:07:00 >> onBufPaneOpen(0:No name)
2020/03/27 14:07:00 << onBufPaneOpen
2020/03/27 14:07:00 >> onBufferOpen(Log)
2020/03/27 14:07:00 << onBufferOpen
2020/03/27 14:07:00 >> init
2020/03/27 14:07:00 << init
2020/03/27 14:07:04 >> onBufferOpen(dummy.lua)
2020/03/27 14:07:04 << onBufferOpen

Showing that onBuffPaneOpen() is not being called for our file 'dummy.lua'.

Specifications

OS: Ubuntu 19.10
Version: 2.0.3-dev.21
Commit hash: 1cf9537
Compiled on March 27, 2020

Happens also with the latest official release 2.0.2.

Start by tracing the Ctrl-O file-opening path and comparing how it dispatches onBufferOpen and onBufPaneOpen. Reproduce the behavior with the supplied dummy.lua plugin and debug log. Done means opening a file after startup triggers onBufPaneOpen with the pane containing the buffer.