Update to Account.set_endpoints set only one specific endpoint

This will allow updating the endpoint for only a single service instead
of both if only one has changed.

src/engine/api/geary-account.vala

@@ -390,14 +390,18 @@ public abstract class Geary.Account : BaseObject {
     }
 
     /**
-     * Sets network endpoints for incoming and outgoing client services.
+     * Sets network endpoints for the incoming or outgoing service.
      *
      * This is called by {@link Engine} after creating the account and
      * if the network configuration changes. Implementations should
      * pass these to their incoming and outgoing client services and
      * restart them as required.
+     *
+     * The service parameter is one of {@link incoming} or {@link
+     * outgoing}.
      */
-    internal abstract void set_endpoints(Endpoint incoming, Endpoint outgoing);
+    internal abstract void set_endpoint(ClientService service,
+                                        Endpoint endpoint);
 
     /** Fires a {@link opened} signal. */
     protected virtual void notify_opened() {

src/engine/api/geary-engine.vala

@@ -368,10 +368,12 @@ public class Geary.Engine : BaseObject {
         Endpoint imap = get_shared_endpoint(
             config.service_provider, config.imap
         );
+        account.set_endpoint(account.incoming, imap);
+
         Endpoint smtp = get_shared_endpoint(
             config.service_provider, config.smtp
         );
-        account.set_endpoints(imap, smtp);
+        account.set_endpoint(account.outgoing, smtp);
 
         account_instances.set(config.id, account);
         return account;

src/engine/imap-engine/imap-engine-generic-account.vala

@@ -558,9 +558,17 @@ private abstract class Geary.ImapEngine.GenericAccount : Geary.Account {
         return (map.size == 0) ? null : map;
     }
 
-    internal override void set_endpoints(Endpoint incoming, Endpoint outgoing) {
-        this.imap.set_endpoint_restart.begin(incoming, this.open_cancellable);
-        this.smtp.set_endpoint_restart.begin(outgoing, this.open_cancellable);
+    internal override void set_endpoint(ClientService service,
+                                        Endpoint endpoint) {
+        if (service == this.incoming) {
+            this.imap.set_endpoint_restart.begin(
+                endpoint, this.open_cancellable
+            );
+        } else if (service == this.outgoing) {
+            this.smtp.set_endpoint_restart.begin(
+                endpoint, this.open_cancellable
+            );
+        }
     }
 
     /**

test/engine/api/geary-account-mock.vala

@@ -230,9 +230,10 @@ public class Geary.MockAccount : Account, MockObject {
         );
     }
 
-    internal override void set_endpoints(Endpoint incoming, Endpoint outgoing) {
+    internal override void set_endpoint(ClientService service,
+                                        Endpoint endpoint) {
         try {
-            void_call("set_endpoints", {incoming, outgoing});
+            void_call("set_endpoint", {service, endpoint});
         } catch (GLib.Error err) {
             // oh well
         }