Filter out empty glob patterns to "glob" command (#6707)

* Filter out empty glob patterns

An empty argument to the "glob" command will now produce an empty result.
Working towards nushell/nushell#6653.

* Run `cargo fmt --all`

Just autoformatted the repo so that CI passes and we have a consistent code
format across modules.

* Treat empty glob argument as error

The glob command will now report an empty string argument as an error instead
of silently ignoring it.

See https://github.com/nushell/nushell/pull/6707#discussion_r993345013.

* Add tests for glob command

Two small tests for the glob command, one to check that the empty string errors
it, and another to sanity check the '*' glob, have been added.

* Rename glob sanity check star test

Co-authored-by: Kyle Anderson <kyle.anderson@uwaterloo.ca>

crates/nu-command/src/filesystem/glob.rs

@@ -99,6 +99,16 @@ impl Command for Glob {
         let glob_pattern: Spanned<String> = call.req(engine_state, stack, 0)?;
         let depth = call.get_flag(engine_state, stack, "depth")?;
 
+        if glob_pattern.item.is_empty() {
+            return Err(ShellError::GenericError(
+                "glob pattern must not be empty".to_string(),
+                "".to_string(),
+                Some(glob_pattern.span),
+                Some("add characters to the glob pattern".to_string()),
+                Vec::new(),
+            ));
+        }
+
         let folder_depth = if let Some(depth) = depth {
             depth
         } else {