Fix the waiting status display for synchronous operations

Commit 4f0393f97b caused a regression: for operations that use
WithWaitingStatusSync (examples are squashing fixups, moving commits up or down,
cherry-picking, creating fixup commits, and more), the waiting status wouldn't
show during the operation; however, it would show after the operation was done,
and then linger forever.

The cause: since 4f0393f97b, layout sizes the bottom line from the actual
content of the AppStatus view rather than from the status manager. The async
render path keeps the view in sync (it sets the buffer on the first tick and
clears it to "" when the status ends), but the sync path used by
WithWaitingStatusSync did not:

- It called ForceLayoutAndRedraw before writing anything to the view, so layout
  saw an empty buffer and left no room; the status never appeared during the
  operation.
- When the operation finished it just broke out of the loop, leaving the last
  spinner frame in the buffer. Every subsequent layout kept reserving room for
  that stale content, so the status stuck around forever.

Fix this by writing the status into the view before the initial layout, and
clearing it again when stopping.

pkg/gui/controllers/helpers/app_status_helper.go

@@ -126,6 +126,13 @@ func (self *AppStatusHelper) renderAppStatusSync(stop chan struct{}) {
 		ticker := time.NewTicker(time.Millisecond * time.Duration(self.c.UserConfig().Gui.Spinner.Rate))
 		defer ticker.Stop()
 
+		// Write the status into the view before the first layout below, so that
+		// layout (which sizes the bottom line based on the actual content of the
+		// AppStatus view) leaves room for it and it shows right away. The ticker
+		// only updates the spinner frame using ForceFlushViewsContentOnly, so this
+		// doesn't re-layout.
+		self.setAppStatusContent()
+
 		// Forcing a re-layout and redraw after we added the waiting status;
 		// this is needed in case the gui.showBottomLine config is set to false,
 		// to make sure the bottom line appears. It's also useful for redrawing
@@ -148,6 +155,14 @@ func (self *AppStatusHelper) renderAppStatusSync(stop chan struct{}) {
 				}
 				_ = self.c.GocuiGui().ForceFlushViewsContentOnly(bottomLineViews)
 			case <-stop:
+				// Clear the status from the view and re-layout, otherwise the
+				// stale content would keep layout reserving room for it forever.
+				// The UI thread is free again at this point, so we go through
+				// OnUIThread like the async renderAppStatus does.
+				self.c.OnUIThread(func() error {
+					self.c.SetViewContent(self.c.Views().AppStatus, "")
+					return nil
+				})
 				break outer
 			}
 		}