fixed a bug in DNS helper code. fixes #1130

src/main/java/eu/siacs/conversations/utils/DNSHelper.java

@@ -121,7 +121,7 @@ public class DNSHelper {
 					while (p > 0) {
 						p -= s.get(i++).getPriority();
 					}
-					i--;
+					if (i>0) i--;
 					// remove is expensive, but we have only a few entries
 					// anyway
 					SRV srv = s.remove(i);

src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java

@@ -204,7 +204,7 @@ public class XmppConnection implements Runnable {
 					&& "nosrv".equals(result.getString("error", null))) {
 				socket = new Socket(account.getServer().getDomainpart(), 5222);
 			} else {
-				throw new IOException("timeout in dns");
+				throw new IOException("unhandled exception in DNS resolver");
 			}
 			final OutputStream out = socket.getOutputStream();
 			tagWriter.setOutputStream(out);