Fix Crash on text editor right click

Fixes Crashes N  and P
Missing nullcheck, my bad
Never expected there not to be a menu segment url when a menu is open

indra/llui/lltexteditor.cpp

@@ -375,7 +375,7 @@ LLTextEditor::~LLTextEditor()
 const std::string& LLTextEditor::getMenuSegmentUrl() const
 {
 	auto segment = getSegmentAtLocalPos(mLastContextMenuX, mLastContextMenuY);
-	auto style = segment->getStyle();
+	auto style = segment ? segment->getStyle() : nullptr;
 	return style ? style->getLinkHREF() : LLStringUtil::null;
 }