patch 8.0.0212: buffer for key name may be too small

Problem:    The buffer used to store a key name theoreticaly could be too
            small. (Coverity)
Solution:   Count all possible modifier characters.  Add a check for the
            length just in case.

src/keymap.h

@@ -482,9 +482,10 @@ enum key_extra
 
 /*
  * The length of the longest special key name, including modifiers.
- * Current longest is <M-C-S-T-4-MiddleRelease> (length includes '<' and '>').
+ * Current longest is <M-C-S-T-D-A-4-ScrollWheelRight> (length includes '<' and
+ * '>').
  */
-#define MAX_KEY_NAME_LEN    25
+#define MAX_KEY_NAME_LEN    32
 
 /* Maximum length of a special key event as tokens.  This includes modifiers.
  * The longest event is something like <M-C-S-T-4-LeftDrag> which would be the