Description:
Calc becomes completely unresponsive with the one specific use of the 'Find & Replace' option.
When 'Find All' results in some matches, the 'Search Results' dialog opens up highlighting the matches in the column(s) selected.
If you now close the 'Search Results' dialog and try searching another pattern using the same 'Find & Replace' dialog, the entire application becomes unresponsive in case the searched pattern does not exist in the searched column(s).
Memory consumption of LibreOffice shoots up from 50MB to about 5.5GB and after some time it shows the searched text in red indicating that the pattern is not found.
However it continues to use CPU (one core) and continues to be extremely sluggish/unresponsive.


Steps to Reproduce:
1. Open any new or existing spreadsheet in Calc
2. Enter "one" in A1 and "two" in A2 (without quotes)
3. Select column A by clicking on 'A' in the header
4. Open "Find & Replace" in the Edit Menu (or Ctrl+H)
5. In the "Find" text box type "two" (without quotes)
6. Click on "Find All"
7. A2 is highlighted now to show the match
8. Close the "Search Results" dialog that pops up
9. Select column A again (as in step 2) by clicking on 'A' in the header
10. In the "Find & Replace" dialog that is still open, in the "Find" text box type "three"
11. Click on "Find All"

Actual Results:
Calc hangs consuming more than 5 GBs of RAM and stays unresponsive even after displaying that no matches are found after a while

Expected Results:
Calc should immediately respond with the indication that the match is not found in the document and NOT consume 5 GBs of RAM


Reproducible: Always


User Profile Reset: Yes



Additional Info:
Version: 6.4.4.2 (x64)
Build ID: 3d775be2011f3886db32dfd395a6a6d1ca2630ff
CPU threads: 12; OS: Windows 10.0 Build 18363; UI render: default; VCL: win; 
Locale: en-US (en_US); UI-Language: en-US
Calc: threaded