Make image scaling command aware of user units (#7222)

* Image: image scaling command is user unit aware ; fixes #6118

- if unitless value entered, InputField uses user choosen base unit
 Before change, always used FC core base unit
 Only applies to GUI user entered values, value changed programmatically still ...
 ... considered in core base unit if applied unitless

src/Gui/InputField.cpp

@@ -642,6 +642,19 @@ void InputField::focusInEvent(QFocusEvent *event)
 
 void InputField::focusOutEvent(QFocusEvent *event)
 {
+    try {
+        if (Quantity::parse(this->text()).getUnit().isEmpty()) {
+            // if user didn't enter a unit, we virtually compensate
+            // the multiplication factor induced by user unit system
+            double factor;
+            QString unitStr;
+            actQuantity.getUserString(factor, unitStr);
+            actQuantity = actQuantity * factor;
+        }
+    }
+    catch (const Base::ParserError& e) {
+        // do nothing, let apply the last known good value
+    }
     this->setText(actQuantity.getUserString());
     QLineEdit::focusOutEvent(event);
 }