Fix lock logic in timers handlers.

[strike-kokhotnikov]

Description

Possible fix of lock logic in timer handlers.

What

Change locking condition.

Why ?

Crash of program, which uses libvma.

How ?

Trivial change

Change type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Tests
• Other

Check list

• Code follows the style de facto guidelines of this project
• Comments have been inserted in hard to understand places
• Documentation has been updated (if necessary)
• Test has been added (if possible)

[svc-nbu-swx-media]

Can one of the admins verify this patch?

[strike-kokhotnikov]

Closed in favor of #1136