patch 8.2.3273: autocmd test fails

Problem:    Autocmd test fails.
Solution:   Require white space before the "{" that starts a block.
diff --git a/src/userfunc.c b/src/userfunc.c
index 01c44d4..5cb3d92 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -901,7 +901,7 @@
 		end = p + STRLEN(p) - 1;
 		while (end > p && VIM_ISWHITE(*end))
 		    --end;
-		if (end > p && *end == '{')
+		if (end > p + 1 && *end == '{' && VIM_ISWHITE(end[-1]))
 		{
 		    int	    is_block;