replace insecure use of eval() with proper use of units

src/Mod/Image/ImageTools/_CommandImageScaling.py

@@ -138,11 +138,13 @@ def cmdCreateImageScaling(name):
         def accept(self):
             sel = FreeCADGui.Selection.getSelection()
             try:
-                locale=QtCore.QLocale.system()
-                #d, ok = locale.toFloat(str(eval(self.lineEdit.text())))
                 try:
-                    d = float(str(eval(self.lineEdit.text().replace(',','.'))))
-                    ok = True
+                    q = FreeCAD.Units.parseQuantity(self.lineEdit.text())
+                    d = q.Value
+                    if q.Unit == FreeCAD.Units.Unit(): # plain number
+                        ok = True
+                    elif q.Unit == FreeCAD.Units.Length:
+                        ok = True
                 except:
                     ok = False
                 if not ok: