Skip empty AppliedPatchSets for sending changes.

src/snapshot/patch.rs

@@ -19,7 +19,7 @@ pub struct PatchSet {
     pub updated_instances: Vec<PatchUpdate>,
 }
 
-impl<'a> PatchSet {
+impl PatchSet {
     pub fn new() -> Self {
         PatchSet {
             removed_instances: Vec::new(),
@@ -76,6 +76,10 @@ impl AppliedPatchSet {
             updated: Vec::new(),
         }
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.removed.is_empty() && self.added.is_empty() && self.updated.is_empty()
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]