Code factoring: introduce BufferView::busy()

The WorkArea should not have to look at details of the undo stack.
No change intended.

src/Buffer.cpp

@@ -802,6 +802,12 @@ Undo & Buffer::undo()
 }
 
 
+Undo const & Buffer::undo() const
+{
+	return d->undo_;
+}
+
+
 void Buffer::setChild(DocIterator const & dit, Buffer * child)
 {
 	d->children_positions[child] = dit;

src/Buffer.h

@@ -651,6 +651,8 @@ public:
 
 	///
 	Undo & undo();
+	///
+	Undo const & undo() const;
 
 	/// This function is called when the buffer is changed.
 	void changed(bool update_metrics) const;

src/BufferView.cpp

@@ -3527,6 +3527,12 @@ void BufferView::checkCursorScrollOffset()
 }
 
 
+bool BufferView::busy() const
+{
+	return buffer().undo().activeUndoGroup();
+}
+
+
 void BufferView::draw(frontend::Painter & pain, bool paint_caret)
 {
 	if (height_ == 0 || width_ == 0)

src/BufferView.h

@@ -339,6 +339,8 @@ public:
 	/// the shape of the caret
 	frontend::CaretGeometry const & caretGeometry() const;
 
+	/// Returns true when the BufferView is not ready for drawing
+	bool busy() const;
 	///
 	void draw(frontend::Painter & pain, bool paint_caret);
 

src/frontends/qt/GuiWorkArea.cpp

@@ -39,7 +39,6 @@
 #include "LyXVC.h"
 #include "Text.h"
 #include "TextMetrics.h"
-#include "Undo.h"
 #include "version.h"
 
 #include "support/convert.h"
@@ -311,8 +310,7 @@ void GuiWorkArea::startBlinkingCaret()
 
 	// Don't start blinking if the cursor isn't on screen, unless we
 	// are not ready to know whether the cursor is on screen.
-	if (!d->buffer_view_->buffer().undo().activeUndoGroup()
-	    && !d->buffer_view_->caretInView())
+	if (!d->buffer_view_->busy() && !d->buffer_view_->caretInView())
 		return;
 
 	d->showCaret();
@@ -498,8 +496,7 @@ void GuiWorkArea::Private::updateCaretGeometry()
 {
 	// we cannot update geometry if not ready and we do not need to if
 	// caret is not in view.
-	if (buffer_view_->buffer().undo().activeUndoGroup()
-	    || !buffer_view_->caretInView())
+	if (buffer_view_->busy() || !buffer_view_->caretInView())
 		return;
 
 
@@ -1240,7 +1237,7 @@ void GuiWorkArea::paintEvent(QPaintEvent * ev)
 	// Do not trigger the painting machinery if we are not ready (see
 	// bug #10989). The second test triggers when in the middle of a
 	// dispatch operation.
-	if (view().busy() || d->buffer_view_->buffer().undo().activeUndoGroup()) {
+	if (view().busy() || d->buffer_view_->busy()) {
 		// Since the screen may have turned black at this point, our
 		// backing store has to be copied to screen. This is a no-op
 		// except when our drawing strategy is "backingstore" (macOS,