patch 9.0.1234: the code style has to be checked manually

Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.
diff --git a/src/digraph.c b/src/digraph.c
index 97a72e1..ac51d50 100644
--- a/src/digraph.c
+++ b/src/digraph.c
@@ -2093,7 +2093,8 @@
 
     if (has_mbyte)
 	buf[(*mb_char2bytes)(code, buf)] = NUL;
-    else {
+    else
+    {
 	buf[0] = code;
 	buf[1] = NUL;
     }