LineEdit: fix placeholder text affected by secret

(cherry picked from commit e64c473bc9792a46196be26b30c39a90f92cace6)

scene/gui/line_edit.cpp

@@ -639,8 +639,8 @@ void LineEdit::_notification(int p_what) {
 				if (char_ofs >= t.length())
 					break;
 
-				CharType cchar = pass ? '*' : t[char_ofs];
-				CharType next = pass ? '*' : t[char_ofs + 1];
+				CharType cchar = (pass && !text.empty()) ? '*' : t[char_ofs];
+				CharType next = (pass && !text.empty()) ? '*' : t[char_ofs + 1];
 				int char_width = font->get_char_size(cchar, next).width;
 
 				// end of widget, break!