Assert failure - Invalid target reg size

**Describe the bug**

I'm getting this assert failure when trying out Dr. Memory on a process that is seg faulting. It seems to not reach the code that seg faults and fails before that.

**To Reproduce**
On Windows (mine is 10.0.18363) using rustc 1.43.1:

[dprint_seg_fault.zip](https://github.com/DynamoRIO/drmemory/files/4740973/dprint_seg_fault.zip)

```
# download zip above, extract then
cd crates/dprint
cargo build --release
cd ../../
drmemory -debug -dr_debug -- target\release\dprint.exe check crates\dprint\test.ts
```

Output:

[results.txt](https://github.com/DynamoRIO/drmemory/files/4698646/results.txt)

- Does the problem go away when running in light mode (pass `-light` to Dr. Memory)?
No
- Does the problem go away when running with the options `-leaks_only -no_count_leaks -no_track_allocs`?
No
- Does the problem go away when running under plain DynamoRIO? Do this by running `dynamorio/bin32/drrun -- ` or `dynamorio/bin64/drrun -- ` depending on the bitwidth of your applicaiton. (Ignore warnings about "incomplete installation".)
Sorry, not sure what this is.
- What happens with the debug version of Dr. Memory and of its underlying engine DynamoRIO? Try this by passing `-debug -dr_debug -pause_at_assert`. Are any messages reported?
Yes, same as what's reported in this issue

**Screenshots or Pasted Text**


**Versions**
- What version of Dr. Memory are you using? 2.3.0 -- build 1, also tried 2.3.18352
- Does the latest build from
https://github.com/DynamoRIO/drmemory/wiki/Latest-Build solve the problem? No, but it has an additional "ERROR: Failed to find "main" for limiting memory dump" then continues on with the same assertion above.
- What operating system version are you running on? 10.0.18363
- Is your application 32-bit or 64-bit? 64.

Thank you!