vim-patch:8.2.0039: memory access error when "z=" has no suggestions

Problem:    Memory access error when "z=" has no suggestions.
Solution:   Check for negative index.
569fea2c31

src/nvim/spell.c

@@ -5761,7 +5761,9 @@ cleanup_suggestions (
         xfree(stp[i].st_word);
       }
       gap->ga_len = keep;
-      return stp[keep - 1].st_score;
+      if (keep >= 1) {
+        return stp[keep - 1].st_score;
+      }
     }
   }
   return maxscore;