[LyX/master] Fix crash after 24926b2e239.

[Richard Kimberly Heck]

commit 104fdcc9be40df19d50cddad7f8ae9ab63bbf5f7
Author: Richard Kimberly Heck <rikiheck at lyx.org>
Date:   Sat Mar 28 15:23:13 2020 -0400

    Fix crash after 24926b2e239.
    
    The matched element may not have a parent. I guess the old version of
    setExpanded too care of that. Now we have to do so.
---
 src/frontends/qt/GuiPrefs.cpp |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/src/frontends/qt/GuiPrefs.cpp b/src/frontends/qt/GuiPrefs.cpp
index d716d85..98aa0c1 100644
--- a/src/frontends/qt/GuiPrefs.cpp
+++ b/src/frontends/qt/GuiPrefs.cpp
@@ -3266,7 +3266,8 @@ void PrefShortcuts::on_searchLE_textEdited()
 	for (int i = 0; i < matched.size(); ++i)
 		if (!isAlwaysHidden(*matched[i])) {
 			matched[i]->setHidden(false);
-			matched[i]->parent()->setExpanded(true);
+			if (matched[i]->parent())
+				matched[i]->parent()->setExpanded(true);
 		}
 }