Fix empty folder/no matching search UI not showing up.

This fixes a regression introduced by commit 0ea1fe6.

* src/engine/app/app-conversation-monitor.vala (ConversationMonitor):
  Signal scan_complete from the same method call that we signal
  scan_started, so that a) we know it will get fired, even if no messages
  are loaded (the issue introduced by 0ea1fe6) and b) so we can get rid
  of the inside_scan complexity.

src/engine/app/app-conversation-monitor.vala

@@ -50,15 +50,15 @@ public class Geary.App.ConversationMonitor : BaseObject {
         Geary.Email.Field.FLAGS | Geary.Email.Field.DATE;
 
 
-    private class ProcessJobContext : BaseObject {
-        public Gee.HashMap<Geary.EmailIdentifier, Geary.Email> emails
-            = new Gee.HashMap<Geary.EmailIdentifier, Geary.Email>();
+    private struct ProcessJobContext {
 
-        public bool inside_scan;
+        public Gee.Map<Geary.EmailIdentifier,Geary.Email> emails;
 
-        public ProcessJobContext(bool inside_scan) {
-            this.inside_scan = inside_scan;
+
+        public ProcessJobContext() {
+            this.emails = new Gee.HashMap<Geary.EmailIdentifier,Geary.Email>();
         }
+
     }
 
 
@@ -402,6 +402,7 @@ public class Geary.App.ConversationMonitor : BaseObject {
         }
 
         int load_count = 0;
+        GLib.Error? scan_error = null;
         try {
             Gee.Collection<Geary.Email>? messages =
                 yield this.base_folder.list_email_by_id_async(
@@ -416,12 +417,16 @@ public class Geary.App.ConversationMonitor : BaseObject {
                     this.window.add(email.id);
                 }
 
-                yield process_email_async(messages, new ProcessJobContext(true));
+                yield process_email_async(messages, ProcessJobContext());
             }
+        } catch (GLib.Error err) {
+            scan_error = err;
+        }
 
-        } catch (Error err) {
-            notify_scan_completed();
-            throw err;
+        notify_scan_completed();
+
+        if (scan_error != null) {
+            throw scan_error;
         }
 
         return load_count;
@@ -437,6 +442,7 @@ public class Geary.App.ConversationMonitor : BaseObject {
             flags |= Folder.ListFlags.LOCAL_ONLY;
         }
 
+        GLib.Error? scan_error = null;
         try {
             Gee.Collection<Geary.Email>? messages =
                 yield this.base_folder.list_email_by_sparse_id_async(
@@ -448,11 +454,16 @@ public class Geary.App.ConversationMonitor : BaseObject {
                     this.window.add(email.id);
                 }
 
-                yield process_email_async(messages, new ProcessJobContext(true));
+                yield process_email_async(messages, ProcessJobContext());
             }
-        } catch (Error err) {
-            notify_scan_completed();
-            throw err;
+        } catch (GLib.Error err) {
+            scan_error = err;
+        }
+
+        notify_scan_completed();
+
+        if (scan_error != null) {
+            throw scan_error;
         }
     }
 
@@ -524,7 +535,7 @@ public class Geary.App.ConversationMonitor : BaseObject {
 
         if (emails != null && !emails.is_empty) {
             debug("Fetched %d relevant emails locally", emails.size);
-            yield process_email_async(emails, new ProcessJobContext(false));
+            yield process_email_async(emails, ProcessJobContext());
         }
     }
 
@@ -727,9 +738,6 @@ public class Geary.App.ConversationMonitor : BaseObject {
             foreach (Conversation conversation in appended.get_keys())
                 notify_conversation_appended(conversation, appended.get(conversation));
         }
-
-        if (job.inside_scan)
-            notify_scan_completed();
     }
 
     private async void expand_conversations_async(Gee.Set<RFC822.MessageID> needed_message_ids,

test/engine/app/app-conversation-monitor-test.vala

@@ -56,6 +56,11 @@ class Geary.App.ConversationMonitorTest : TestCase {
         );
         Cancellable test_cancellable = new Cancellable();
 
+        bool saw_scan_started = false;
+        bool saw_scan_completed = false;
+        monitor.scan_started.connect(() => { saw_scan_started = true; });
+        monitor.scan_completed.connect(() => { saw_scan_completed = true; });
+
         this.base_folder.expect_call(
             "open_async",
             { MockObject.int_arg(Folder.OpenFlags.NONE), test_cancellable }
@@ -68,11 +73,19 @@ class Geary.App.ConversationMonitorTest : TestCase {
         );
         monitor.start_monitoring_async.end(async_result());
 
+        // Process all of the async tasks arising from the open
+        while (this.main_loop.pending()) {
+            this.main_loop.iteration(true);
+        }
+
         monitor.stop_monitoring_async.begin(
             test_cancellable, (obj, res) => { async_complete(res); }
         );
         monitor.stop_monitoring_async.end(async_result());
 
+        assert_true(saw_scan_started, "scan_started not fired");
+        assert_true(saw_scan_completed, "scan_completed not fired");
+
         this.base_folder.assert_expectations();
     }