fixed bug that prevented newly opened conversations to load the entire history via mam. fixes #1328

src/main/java/eu/siacs/conversations/entities/Conversation.java

@@ -673,6 +673,10 @@ public class Conversation extends AbstractEntity implements Blockable {
 		}
 	}
 
+	public void resetLastMessageTransmitted() {
+		this.setAttribute(ATTRIBUTE_LAST_MESSAGE_TRANSMITTED,String.valueOf(-1));
+	}
+
 	public boolean setLastMessageTransmitted(long value) {
 		long before = getLastMessageTransmitted();
 		if (value - before > 1000) {

src/main/java/eu/siacs/conversations/services/MessageArchiveService.java

@@ -68,7 +68,15 @@ public class MessageArchiveService implements OnAdvancedStreamFeaturesLoaded {
 	}
 
 	public Query query(final Conversation conversation) {
-		return query(conversation,conversation.getAccount().getXmppConnection().getLastSessionEstablished());
+		if (conversation.getLastMessageTransmitted() < 0 && conversation.countMessages() == 0) {
+			return query(conversation,
+					0,
+					System.currentTimeMillis());
+		} else {
+			return query(conversation,
+					conversation.getLastMessageTransmitted(),
+					conversation.getAccount().getXmppConnection().getLastSessionEstablished());
+		}
 	}
 
 	public Query query(final Conversation conversation, long end) {

src/main/java/eu/siacs/conversations/services/XmppConnectionService.java

@@ -2545,6 +2545,7 @@ public class XmppConnectionService extends Service implements OnPhoneContactsLoa
 	public void clearConversationHistory(final Conversation conversation) {
 		conversation.clearMessages();
 		conversation.setHasMessagesLeftOnServer(false); //avoid messages getting loaded through mam
+		conversation.resetLastMessageTransmitted();
 		new Thread(new Runnable() {
 			@Override
 			public void run() {