Fix stylesheet warnings introduced by 3b330ee (#3610)

Fixes regression introduced by 3b330ee.
The previous changes could add an invalid style
sheet to PasswordEdit's QLineEdit.

src/gui/PasswordEdit.cpp

@@ -94,24 +94,23 @@ bool PasswordEdit::passwordsEqual() const
 
 void PasswordEdit::updateStylesheet()
 {
-    QString stylesheet("QLineEdit { background: %1; }");
+    const QString stylesheetTemplate("QLineEdit { background: %1; }");
 
     if (m_basePasswordEdit && !passwordsEqual()) {
         bool isCorrect = true;
         if (m_basePasswordEdit->text().startsWith(text())) {
-            stylesheet = stylesheet.arg(CorrectSoFarColor.name());
+            setStyleSheet(stylesheetTemplate.arg(CorrectSoFarColor.name()));
         } else {
-            stylesheet = stylesheet.arg(ErrorColor.name());
+            setStyleSheet(stylesheetTemplate.arg(ErrorColor.name()));
             isCorrect = false;
         }
         m_correctAction->setVisible(isCorrect);
         m_errorAction->setVisible(!isCorrect);
     } else {
         m_correctAction->setVisible(false);
         m_errorAction->setVisible(false);
+        setStyleSheet("");
     }
-
-    setStyleSheet(stylesheet);
 }
 
 void PasswordEdit::autocompletePassword(const QString& password)