tree-wide: use is_empty() and similar

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

src/api2/access/mod.rs

@@ -92,7 +92,7 @@ fn authenticate_user(
                 if *name == privilege_name {
                     let mut path_vec = Vec::new();
                     for part in path.split('/') {
-                        if part != "" {
+                        if !part.is_empty() {
                             path_vec.push(part);
                         }
                     }

src/api2/tape/restore.rs

@@ -215,7 +215,7 @@ pub fn restore(
     let store_map = DataStoreMap::try_from(store)
         .map_err(|err| format_err!("cannot parse store mapping: {}", err))?;
     let used_datastores = store_map.used_datastores();
-    if used_datastores.len() == 0 {
+    if used_datastores.is_empty() {
         bail!("no datastores given");
     }