mapproject(): "GMT: Failure to open virtual file"

I'm getting the above error after I call `mapproject()` exactly 250,000 times in a row. I would like to call it many more times!

If I call it again from the REPL after my program crashes, it gives the same error. I have to restart Julia to get rid of the message.

```
julia> versioninfo()
Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
Official https://julialang.org/ release
Platform Info:
OS: macOS (arm64-apple-darwin24.0.0)
CPU: 16 × Apple M4 Max
WORD_SIZE: 64
LLVM: libLLVM-16.0.6 (ORCJIT, apple-m1)
Threads: 12 default, 0 interactive, 6 GC (on 12 virtual cores)
Environment:
JULIA_NUM_THREADS = auto
JULIA_EDITOR = code
JULIA_VSCODE_REPL = 1
```

This happens in both GMT.jl 1.31.1 and 1.32.0.