patch 8.2.2972: "%bd" tries to delete popup window buffers, which fails

Problem:    "%bd" tries to delete popup window buffers, which fails. (Ralf
            Schandl)
Solution:   Do not try to delete a popup window buffer. (closes #8349)
diff --git a/src/vim.h b/src/vim.h
index 61afe97..e1e68f9 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -994,6 +994,10 @@
 #define DOBUF_LAST	2	// "count" buffer from last buffer
 #define DOBUF_MOD	3	// "count" mod. buffer from current buffer
 
+// Values for flags argument of do_buffer()
+#define DOBUF_FORCEIT	1	// :cmd!
+#define DOBUF_NOPOPUP	2	// skip popup window buffers
+
 // Values for sub_cmd and which_pat argument for search_regcomp()
 // Also used for which_pat argument for searchit()
 #define RE_SEARCH	0	// save/use pat in/from search_pattern