[LyX/master] Prevent infinite loop with instant search on Mac (#12161)

[Juergen Spitzmueller]

commit 939dc4076fe577a40dea99ec668c92c7a6a1d711
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sun Feb 28 17:34:42 2021 +0100

    Prevent infinite loop with instant search on Mac (#12161)
    
    The search dialog was repeatedly feeded with the same string, and a
    new search was triggered.
---
 src/frontends/qt/GuiSearch.cpp |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/src/frontends/qt/GuiSearch.cpp b/src/frontends/qt/GuiSearch.cpp
index 169c7aa..54e4ea6 100644
--- a/src/frontends/qt/GuiSearch.cpp
+++ b/src/frontends/qt/GuiSearch.cpp
@@ -417,7 +417,9 @@ void GuiSearchWidget::showEvent(QShowEvent * e)
 void GuiSearchWidget::findBufferChanged()
 {
 	docstring search = theClipboard().getFindBuffer();
-	if (!search.empty()) {
+	// update from find buffer, but only if the strings differs (else we
+	// might end up in loops with search as you type)
+	if (!search.empty() && toqstr(search) != findCO->lineEdit()->text()) {
 		LYXERR(Debug::CLIPBOARD, "from findbuffer: " << search);
 		findCO->lineEdit()->selectAll();
 		findCO->lineEdit()->insert(toqstr(search));