Reproduction steps:
1. Open the attached project "ReproProj"
2. Open Font Asset Creator (Window > TextMeshPro > Font Asset Creator)
3. Set Padding to “-2.147484e+09” %
3. Click “Generate Font Atlas“

Expected result: Font atlas is successfully generated
Actual result: Editor crashes

Reproducible with: TMP 4.0.0-pre.2 (2022.3.54f1), uGUI 2.0.0 (6000.0.31f1, 6000.1.0a8)

Testing environment: Windows 10 Enterprise 21H2
Not reproducible on: No other environment tested

First few lines of the Stacktrace:
0x00007FF947E315B9 (Unity) tlsf_free
0x00007FF945947720 (Unity) DynamicHeapAllocator::Deallocate
0x00007FF945955465 (Unity) DelayedPointerDeletionManager::CleanupPendingMainThreadPointersInternal
0x00007FF945954C3B (Unity) DualThreadAllocator<DynamicHeapAllocator>::Allocate
0x00007FF94594638D (Unity) MemoryManager::Allocate

Note:
- Does not reproduce with Padding set to “5” %