Fix normalizePath null call with missing conda

[tl-hbk]

I was trying to use reticulate with a pixi env which only populates conda-meta/history with

// not relevant for pixi but for `conda run -p`

I have options(reticulate.conda_binary = conda) set to a copy of micromamba.exe to handle the conda related operations but when use_python tries to get the conda root/binary info it passes NULL to normalizePath if it can't find conda automatically, which causes the following error Error in path.expand(path) : invalid 'path' argument which is mentioned in #1184

 1: source("src/r/conda.R")
 2: withVisible(eval(ei, envir))
 3: eval(ei, envir)
 4: eval(ei, envir)
 5: conda.R#9: use_python(pixi_env, required = TRUE)
 6: python_config(python)
 7: python_munge_path(python)
 8: get_python_conda_info(python)
 9: normalizePath(conda, winslash = "/", mustWork = FALSE)
10: path.expand(path)

Related issue:
#1650

[t-kalinowski]

Thanks for the PR! Can you please add a NEWS item?

[tl-hbk]

Thanks for the PR! Can you please add a NEWS item?

Sure I'll go ahead and add that

[tl-hbk]

@t-kalinowski the NEWS file has been udpated

[t-kalinowski]

Thank you!