Validate file extension before creating empty file

Move validateConfigFileExtension call before file.CreateEmptyIfNotExists
to avoid creating unnecessary files with invalid extensions on the filesystem.
This addresses the review comment by ensuring validation happens first.

Co-authored-by: dlevy-msft-sql <[email protected]>

Author: Copilot

internal/config/config.go

@@ -26,8 +26,12 @@ func SetFileName(name string) {
 
 	filename = name
 
+	// Validate file extension before creating the file
+	err := validateConfigFileExtension(filename)
+	checkErr(err)
+
 	file.CreateEmptyIfNotExists(filename)
-	err := configureViper(filename)
+	err = configureViper(filename)
 	checkErr(err)
 }