fix(main.rs): Handle file not found error

- Print an error message and exit with code 1 if the file is not found
- Validate file extension and print an error message if it does not have the .xlsx extension

cat_xlsx/src/main.rs

@@ -20,8 +20,14 @@ fn main() -> Result<(), Box<dyn Error>> {
     let path = args.xlsx_file;
     // Check if the file exists
     if !path.exists() {
+        eprintln!("Error: File not found");
+        std::process::exit(1);
+    }
     // Validate file extension
-    if !path.extension().map_or(false, |ext| ext.eq_ignore_ascii_case("xlsx")) {
+    if !path
+        .extension()
+        .map_or(false, |ext| ext.eq_ignore_ascii_case("xlsx"))
+    {
         eprintln!("Error: File must have .xlsx extension");
         std::process::exit(1);
     }