UI: Fix previewLabel styling

Label renders with default styling instead of using dynamic property
because it was already polished.

UI/window-basic-main.cpp

@@ -385,6 +385,7 @@ OBSBasic::OBSBasic(QWidget *parent)
 	statsDock->move(newPos);
 
 	ui->previewLabel->setProperty("themeID", "previewProgramLabels");
+	ui->previewLabel->style()->polish(ui->previewLabel);
 
 	bool labels = config_get_bool(GetGlobalConfig(), "BasicWindow",
 				      "StudioModeLabels");