DAG crashes when selecting another commit while generating very large diff

[mlam19]

Environment

Git Cola 3.6
Windows 10

Steps to reproduce

1. Create a new repository
2. Make an initial commit (commit 1) with large size (my use case was ~3000 files, ~1.4 GB)
3. Make another commit (commit 2) of trivial size
4. Open the repository using git-dag from the terminal
5. Select commit 1 in the Log or Graph area
   • Graph and Files area reflect the selection in <10 seconds
   • Diff area remains +++Loading...
   • DAG window remains responsive (can close the window, use the scrollbars, etc..)
6. Select commit 2 in the Log or Graph area
   • DAG window becomes unresponsive (busy mouse cursor, window title shows "(Not Responding)")
   • Terminal outputs:

Exception in thread Thread-48:
Traceback (most recent call last):
File "threading.py", line 916, in _bootstrap_inner
File "threading.py", line 864, in run
File "subprocess.py", line 1063, in _readerthread
MemoryError

Notes

• DAG window may be closed normally before executing step 6. After step 6, closing the window results in Windows error dialog ("Python is not responding")
• Problem also occurs when closing the Diff area before performing steps 5 and 6