Add warning if no results found by createMergedResultsFile

[MaximMoinat]

Description

If there is no results zip in the given dataFolder when running createMergedResultsFile, it will show that it connects to a database and then exits (see screenshot). This does create a .sqlite file with all necessary results tables, but no records are loaded. Then, when running the Shiny app, I just get the error 'Object databases not found'. This is especially confusing when the result csv's are in the given folder, but for some reason there is no zip of the results.

(Using version 3.1.0)

Suggested fix

Display a warning "No result zip files found", on line 197 here:

CohortDiagnostics/R/Shiny.R

Lines 197 to 212 in 0e3764f

	listOfZipFilesToUpload <-
	list.files(
	path = dataFolder,
	pattern = ".zip",
	full.names = TRUE,
	recursive = TRUE
	)
	for (zipFileName in listOfZipFilesToUpload) {
	uploadResults(
	connectionDetails = connectionDetails,
	schema = "main",
	zipFileName = zipFileName,
	tablePrefix = tablePrefix
	)
	}

[azimov]

Agreed - but i think stopping/throwing an error is better as it will avoid leaving an empty database file in the folder