patch 8.1.1773: the preview popup window may be too far to the right
Problem: The preview popup window may be too far to the right.
Solution: Keep it inside the screen. Also keep the close button and
scrollbar visible if possible.
diff --git a/src/vim.h b/src/vim.h
index 452a9b9..9d7ecf6 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -618,6 +618,8 @@
#define POPF_HIDDEN 2 // popup is not displayed
#define POPF_HANDLED 4 // popup was just redrawn or filtered
#define POPF_CURSORLINE 8 // popup is highlighting at the cursorline
+#define POPF_ON_CMDLINE 16 // popup overlaps command line
+
#ifdef FEAT_TEXT_PROP
# define WIN_IS_POPUP(wp) ((wp)->w_popup_flags != 0)
#else