Allow empty paths to be passed to Stack in debug mode

It can handle it, so let's let it be a no-op.

Author: Byron

gix-fs/src/stack.rs

@@ -63,7 +63,6 @@ impl Stack {
             relative.is_relative(),
             "only index paths are handled correctly here, must be relative"
         );
-        debug_assert!(!relative.to_string_lossy().is_empty(), "empty paths are not allowed");
 
         if self.valid_components == 0 {
             delegate.push_directory(self)?;

gix-fs/tests/stack/mod.rs

@@ -141,5 +141,16 @@ fn delegate_calls_are_consistent() -> crate::Result {
         "the stack is state so keeps thinking it's a directory which is consistent. Git does it differently though."
     );
 
+    s.make_relative_path_current("".as_ref(), &mut r)?;
+    assert_eq!(
+        r,
+        Record {
+            push_dir: 9,
+            dirs: vec![".".into()],
+            push: 14,
+        },
+        "empty-paths reset the tree effectively"
+    );
+
     Ok(())
 }