Single-instance mode breaks opening KDBX files by double click

[phoerious]

When a KeePassXC instance is running and the user double-clicks a KDBX file to open it, the existing KeePassXC instance will be activated, but the file won't be opened.

Expected Behavior

Double-clicking a file should open it in KeePassXC, even if an instance is already running.

Current Behavior

KeePassXC is activated, but file doesn't open. Dragging it into the KeePassXC window works.

Possible Solution

Pass file name to running instance before exiting.

Steps to Reproduce (for bugs)

1. Open KeePassXC (compiled in Release mode)
2. Double-click a KDBX file to open it

Debug Info

KeePassXC - Version 2.3.0-preview
Build Type: PreRelease
Revision: 10bd73c

Libraries:

• Qt 5.9.1
• libgcrypt 1.7.8

Operating system: Ubuntu 17.10
CPU architecture: x86_64
Kernel: linux 4.13.0-36-generic

Enabled extensions:

• Auto-Type
• Browser Integration
• Legacy Browser Integration (KeePassHTTP)
• SSH Agent
• YubiKey

[nemoinis]

This is probably another manifestation: specifying a database name on the command line does not prompt for password/keyfile either. e.g.,
$ keepassxc /path/to/my/database
just starts keepassxc as if /path/to/my/database had not been given.
This happens whether Single-instance mode is on or not.

[phoerious]

Turns out, this is the same issue as #1358.