Description:
o3tl::cow_wrapper<ImplFont, o3tl::UnsafeRefCountingPolicy>::make_unique() leaks memory

Steps to Reproduce:
1. Start the Instruments
2. Choose Memory Leak profile tool
3. Select LibreOffice.app in instdir as target process
4. Click on the record button, LODev is started by the profiling tool
5. Wait for the StartCenter to load.
6. Click on the new Impress document icon to open a Impress document.
7. Choose a template
8. LibreOffice -> Preferences
9. Load/Save -> Set autosave to 1 minute
10. Press OK
11. Wait for the autosave
12. Stop recording (after the closing is fully processed) 
13. Analyse the profile trace.

Actual Results:  
o3tl::cow_wrapper<ImplFont, o3tl::UnsafeRefCountingPolicy>::make_unique() leaks memory

Expected Results:
Shouldn't do that


Reproducible: Always

User Profile Reset: No

Additional Info:
Version: 6.0.0.0.alpha0+
CPU threads: 4; OS: Mac OS X 10.12.4; UI render: default; 
Locale: en-US (en_US.UTF-8); Calc: group

Build from 5 September 



User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0