Crash when two users editing same entry in shared group

[laurencejp]

Overview

When two users are editing the same entry in a shared group and one applies the change before the other, the second user's client will crash.

Steps to Reproduce

1. Create a shared group, can be synchronized or import/export between two users.
2. Enter the edit screen for a specific entry in the group on both clients.
3. Change the password field to something different on both clients.
4. Apply the update on one client and press 'OK'.
5. Press 'Apply' on the second client.

Expected Behavior

The entry now contains the password from the client that pressed 'Apply' second.

Actual Behavior

The client of the user that pressed 'Apply' second crashes with the following error:

Context

Using an unsigned shared group.
The same thing happens whether the group is shared using import/export or synchronized.

KeePassXC - Version 2.6.2
Revision: e9b9582

Qt 5.15.1
Debugging mode is disabled.

Operating system: Windows 10 Version 2004
CPU architecture: x86_64
Kernel: winnt 10.0.19041

Enabled extensions:

• Auto-Type
• Browser Integration
• SSH Agent
• KeeShare (signed and unsigned sharing)
• YubiKey

Cryptographic libraries:
libgcrypt 1.8.6

[droidmonkey]

This occurs because KeeShare merges the database which causes the current entry pointer to go invalid and thus NULL. This will be truly fixed when the edit entry widget is overhauled in 2.7.0. Until then we can band aid the crash by checking for nullptr prior to commit.