patch 8.2.4258: Coverity warns for array overrun

Problem:    Coverity warns for array overrun.
Solution:   Restrict depth to MAXWLEN - 1.
diff --git a/src/spellsuggest.c b/src/spellsuggest.c
index 3cd4535..e21ac80 100644
--- a/src/spellsuggest.c
+++ b/src/spellsuggest.c
@@ -1214,7 +1214,7 @@
 
 // Check the maximum score, if we go over it we won't try this change.
 #define TRY_DEEPER(su, stack, depth, add) \
-	   (depth < MAXWLEN && stack[depth].ts_score + (add) < su->su_maxscore)
+       (depth < MAXWLEN - 1 && stack[depth].ts_score + (add) < su->su_maxscore)
 
 /*
  * Try finding suggestions by adding/removing/swapping letters.
@@ -1373,7 +1373,7 @@
 
 		// At end of a prefix or at start of prefixtree: check for
 		// following word.
-		if (depth < MAXWLEN
+		if (depth < MAXWLEN - 1
 			    && (byts[arridx] == 0 || n == (int)STATE_NOPREFIX))
 		{
 		    // Set su->su_badflags to the caps type at this position.