BF: Enable/disable OK button in Loop properties when text is edited r…

…ather than when button is pressed, meaning it can be re-enabled when a mistake is fixed

psychopy/app/builder/dialogs/__init__.py

@@ -1341,6 +1341,7 @@ def makeConstantsCtrls(self):
                 self.Bind(wx.EVT_BUTTON, self.onBrowseTrialsFile,
                           ctrls.browseCtrl)
                 ctrls.valueCtrl.Bind(wx.EVT_RIGHT_DOWN, self.viewConditions)
+                ctrls.valueCtrl.Bind(wx.EVT_TEXT, self.doValidate)
                 panelSizer.Add(ctrls.nameCtrl, [row, 0])
                 panelSizer.Add(ctrls.valueCtrl, [row, 1])
                 panelSizer.Add(ctrls.browseCtrl, [row, 2])