[LyX/2.2.x] Be a bit more careful about setting and restoring the last reference when we go to and return from labels.

[Richard Heck]

commit c503804eeb9e2606d095f8a7e260d7a3f18c9c9d
Author: Richard Heck <rgh...@lyx.org>
Date:   Sat Jun 18 18:27:51 2016 -0400

    Be a bit more careful about setting and restoring the last reference
    when we go to and return from labels.
    
    (cherry picked from commit 68b60ec529db2e7bfe642bd09902824ea69e2fb5)

diff --git a/src/frontends/qt4/GuiRef.cpp b/src/frontends/qt4/GuiRef.cpp
index 555ccce..795736c 100644
--- a/src/frontends/qt4/GuiRef.cpp
+++ b/src/frontends/qt4/GuiRef.cpp
@@ -118,9 +118,12 @@ void GuiRef::gotoClicked()
        // to which we are going (or from which we are returning) is
        // restored in the dialog. It's a bit of a hack, but it works,
        // and no-one seems to have any better idea.
-       last_reference_ = referenceED->text();
+       bool const toggled = last_reference_.empty();
+       if (toggled)
+               last_reference_ = referenceED->text();
        gotoRef();
-       last_reference_.clear();
+       if (toggled)
+               last_reference_.clear();
 }