Ignore directories in repo that have index errors

[caseymcc]

Gracefully handle repos with index errors.

• skips any directories with indexing issues

[paul-gauthier]

Can you share a traceback of the problem this is trying to solve?

[caseymcc]

When running against the UnrealEngine repo (which is quite large and likely the major issue), I was getting the following

~/projects/UnrealEngine$ aider
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Unable to list files in git repo: index out of range
Is your git repo corrupted?
Unable to read git repository, it may be corrupt?
index out of range

Tracking it down it has something todo with Engine/Build/BatchFiles/Linux although the repo itself looks fine. When the IndexError exception occurs the blob has the following

Blob path: Engine/Build/BatchFiles/Linux
Blob type: tree
Blob size: 792 bytes
Blob SHA-1: 5105a8667c86576bd67920c59df26af801b1285e

adding the above just allows it to skip the directory rather then stopping the repo map.