[PATCHv2 1/6] gdb/tui: convert a window handle `if` into an `assert`

[Andrew Burgess <aburgess@redhat.com>]

It should only be possible to call tui_win_info::refresh_window on a
window with a valid handle member.  To do otherwise would suggest
we're trying to draw to the screen a window which GDB doesn't think is
part of the current layout, which is just wrong.

Currently tui_win_info::refresh_window guards its content with an
`if (handle != NULL)`, but this can be changed to an assert.

A similar assert can be added to
tui_source_window_base::refresh_window, there's no `if` in this
function, which only backs up the reasoning in the first paragraph.

There should be no user-visible changes after this commit.
---
 gdb/tui/tui-wingeneral.c | 13 ++++++-------
 gdb/tui/tui-winsource.c  |  2 ++
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/gdb/tui/tui-wingeneral.c b/gdb/tui/tui-wingeneral.c
index 149ca4efc6e..281c56d475e 100644
--- a/gdb/tui/tui-wingeneral.c
+++ b/gdb/tui/tui-wingeneral.c
@@ -55,13 +55,12 @@ tui_batch_rendering::~tui_batch_rendering ()
 void
 tui_win_info::refresh_window ()
 {
-  if (handle != NULL)
-    {
-      if (suppress_output)
-	wnoutrefresh (handle.get ());
-      else
-	wrefresh (handle.get ());
-    }
+  gdb_assert (handle != nullptr);
+
+  if (suppress_output)
+    wnoutrefresh (handle.get ());
+  else
+    wrefresh (handle.get ());
 }
 
 /* Draw a border around the window.  */
diff --git a/gdb/tui/tui-winsource.c b/gdb/tui/tui-winsource.c
index e3f64892e27..c7149ff7c80 100644
--- a/gdb/tui/tui-winsource.c
+++ b/gdb/tui/tui-winsource.c
@@ -310,6 +310,8 @@ tui_source_window_base::refresh_window ()
 {
   TUI_SCOPED_DEBUG_START_END ("window `%s`", name ());
 
+  gdb_assert (handle != nullptr);
+
   /* tui_win_info::refresh_window would draw the empty background window to
      the screen, potentially creating a flicker.  */
   wnoutrefresh (handle.get ());
-- 
2.25.4