Clear error message when attempting to read non-excel file

[john-ioannides]

As I understand that this package is an improvement of the openxlsx package, I've recently switched one of my codes from the old one to this one,

When attempting to read non-excel files, openxlsx::read.xlsx() gave this clear error:

Error: openxlsx can only read .xlsx or .xlsm files

On the contrary, with the same input, openxlsx2::read_xlsx() gives this rather misleading error:

Error in basename(sheets$Target) : object 'sheets' not found
In addition: Warning message:
In unzip(file, exdir = xmlDir) : error 1 in extracting from zip file

I think a clearer error message would be more suitable.

[JanMarvin]

Hi @john-ioannides , thanks for reaching out. I tried to fix this recently #887, but it looks like this was unsuccessful. Might have to check for the existence of specific files in the zipped file.