qt: fixes #1180

qt/i2pd_qt/I2pdQtUtil.cpp

@@ -0,0 +1,12 @@
+#include "I2pdQtUtil.h"
+
+bool isValidSingleLine(QLineEdit* widget, WrongInputPageEnum inputPage, MainWindow* mainWindow) {
+    bool correct = !widget->text().contains(QRegularExpression("[\r\n]"), nullptr);
+    if(!correct) {
+        mainWindow->highlightWrongInput(
+                    QApplication::tr("Single line input expected, but it's multiline"),
+                    inputPage,
+                    widget);
+    }
+    return correct;
+}