Corrected multiple Yubikey bugs

* Fixed database not showing modified after failed save
* Fixed Yubikey not being redetected after replug
* Fixed single shot challenge resulting in failed saves

src/gui/DatabaseTabWidget.cpp

@@ -363,6 +363,8 @@ bool DatabaseTabWidget::saveDatabase(Database* db)
             emit messageDismissTab();
             return true;
         } else {
+            dbStruct.modified = true;
+            updateTabName(db);
             emit messageTab(tr("Writing the database failed.").append("\n").append(errorMessage),
                             MessageWidget::Error);
             return false;

src/keys/YkChallengeResponseKey.cpp

@@ -50,7 +50,7 @@ QByteArray YkChallengeResponseKey::rawKey() const
  */
 bool YkChallengeResponseKey::challenge(const QByteArray& challenge)
 {
-    return this->challenge(challenge, 1);
+    return this->challenge(challenge, 2);
 }
 
 bool YkChallengeResponseKey::challenge(const QByteArray& challenge, unsigned retries)
@@ -70,8 +70,8 @@ bool YkChallengeResponseKey::challenge(const QByteArray& challenge, unsigned ret
 
         QEventLoop loop;
         QFutureWatcher<YubiKey::ChallengeResult> watcher;
-        watcher.setFuture(future);
         connect(&watcher, SIGNAL(finished()), &loop, SLOT(quit()));
+        watcher.setFuture(future);
         loop.exec();
 
         if (m_blocking) {

src/keys/drivers/YubiKey.cpp

@@ -154,7 +154,7 @@ YubiKey::ChallengeResult YubiKey::challenge(int slot, bool mayBlock, const QByte
     QByteArray paddedChallenge = challenge;
 
     // ensure that YubiKey::init() succeeded
-    if (m_yk == NULL) {
+    if (!init()) {
         m_mutex.unlock();
         return ERROR;
     }