Environment: Fix crash in environment widget

Change-Id: I39b30a73932a6fac67cdb6b07225a4f675346fec
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/libs/utils/environmentdialog.cpp

@@ -157,7 +157,8 @@ QList<EnvironmentItem> EnvironmentDialog::getEnvironmentItems(bool *ok,
                 Polisher polisher)
 {
     EnvironmentDialog dlg(parent);
-    polisher(&dlg);
+    if (polisher)
+        polisher(&dlg);
     dlg.setEnvironmentItems(initial);
     dlg.setPlaceholderText(placeholderText);
     bool result = dlg.exec() == QDialog::Accepted;