Only highlight cursor line after syntax highlighter is finished

This is because cursor line highlight relies on data from syntax
highlighting (to apply background colors)

Author: kovidgoyal

src/calibre/gui2/tweak_book/editor/text.py

@@ -625,14 +625,17 @@ def go_to_anchor(self, anchor):
 
     # Line numbers and cursor line {{{
     def highlight_cursor_line(self):
+        if self.highlighter.is_working:
+            QTimer.singleShot(10, self.highlight_cursor_line)
+            return
         sel = QTextEdit.ExtraSelection()
         sel.format.setBackground(self.palette().alternateBase())
         sel.format.setProperty(QTextFormat.Property.FullWidthSelection, True)
         sel.cursor = self.textCursor()
         sel.cursor.clearSelection()
         self.current_cursor_line = [sel]
 
-        # apply any formats that have a backgroud over the cursor line format
+        # apply any formats that have a background over the cursor line format
         # to ensure they are visible
         c = self.textCursor()
         block = c.block()