fix freeze on MacOS in ColumnViewerEditor

[tobiasmelcher]

cancelEditing cannot be called when shouldFireDoubleClick on mouseDown event returns true

Fixes: https://github.com/eclipse-platform/eclipse.platform.ui/issues/2927

[github-actions[bot]]

Test Results

 1 824 files  ±0   1 824 suites  ±0   1h 37m 11s ⏱️ + 3m 23s  7 918 tests ±0   7 688 ✅  - 2  228 💤 ±0  2 ❌ +2  23 841 runs  ±0  23 091 ✅  - 2  748 💤 ±0  2 ❌ +2 

For more details on these failures, see this check.

Results for commit 07637d6c. ± Comparison against base commit 9a586ab1.