patch 8.2.3530: ":buf \{a}" fails while ":edit \{a}" works

Problem:    ":buf \{a}" fails while ":edit \{a}" works.
Solution:   Unescape "\{". (closes #8917)
diff --git a/src/vim.h b/src/vim.h
index b7a6388..d2e0d9b 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -291,6 +291,7 @@
 #endif
 #ifdef BACKSLASH_IN_FILENAME
 # define PATH_ESC_CHARS ((char_u *)" \t\n*?[{`%#'\"|!<")
+# define BUFFER_ESC_CHARS ((char_u *)" \t\n*?[`%#'\"|!<")
 #else
 # ifdef VMS
     // VMS allows a lot of characters in the file name
@@ -300,6 +301,7 @@
 #  define PATH_ESC_CHARS ((char_u *)" \t\n*?[{`$\\%#'\"|!<")
 #  define SHELL_ESC_CHARS ((char_u *)" \t\n*?[{`$\\%#'\"|!<>();&")
 # endif
+#  define BUFFER_ESC_CHARS ((char_u *)" \t\n*?[`$\\%#'\"|!<")
 #endif
 
 // length of a buffer to store a number in ASCII (64 bits binary + NUL)
@@ -2766,5 +2768,9 @@
 #define UC_BUFFER	1	// -buffer: local to current buffer
 #define UC_VIM9		2	// {} argument: Vim9 syntax.
 
+// flags used by vim_strsave_escaped()
+#define VSE_NONE	0
+#define VSE_SHELL	1	// escape for a shell command
+#define VSE_BUFFER	2	// escape for a ":buffer" command
 
 #endif // VIM__H