patch 9.0.0272: BufReadCmd not triggered when loading a "nofile" buffer

Problem:    BufReadCmd not triggered when loading a "nofile" buffer. (Maxim
            Kim)
Solution:   Call readfile() but bail out before reading a file.
            (closes #10983)
diff --git a/src/vim.h b/src/vim.h
index 9445fa2..05b6632 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1006,6 +1006,7 @@
 #define READ_KEEP_UNDO	0x20	// keep undo info
 #define READ_FIFO	0x40	// read from fifo or socket
 #define READ_NOWINENTER 0x80	// do not trigger BufWinEnter
+#define READ_NOFILE	0x100	// do not read a file, do trigger BufReadCmd
 
 // Values for change_indent()
 #define INDENT_SET	1	// set indent