patch 8.2.0387: error for possible NULL argument to qsort()

Problem:    Error for possible NULL argument to qsort().
Solution:   Don't call qsort() when there is nothing to sort. (Dominique
            Pelle, closes #5780)
diff --git a/src/spellsuggest.c b/src/spellsuggest.c
index fdd549e..267a4a5 100644
--- a/src/spellsuggest.c
+++ b/src/spellsuggest.c
@@ -3719,17 +3719,22 @@
     suggest_T   *stp = &SUG(*gap, 0);
     int		i;
 
-    // Sort the list.
-    qsort(gap->ga_data, (size_t)gap->ga_len, sizeof(suggest_T), sug_compare);
-
-    // Truncate the list to the number of suggestions that will be displayed.
-    if (gap->ga_len > keep)
+    if (gap->ga_len > 0)
     {
-	for (i = keep; i < gap->ga_len; ++i)
-	    vim_free(stp[i].st_word);
-	gap->ga_len = keep;
-	if (keep >= 1)
-	    return stp[keep - 1].st_score;
+	// Sort the list.
+	qsort(gap->ga_data, (size_t)gap->ga_len, sizeof(suggest_T),
+								  sug_compare);
+
+	// Truncate the list to the number of suggestions that will be
+	// displayed.
+	if (gap->ga_len > keep)
+	{
+	    for (i = keep; i < gap->ga_len; ++i)
+		vim_free(stp[i].st_word);
+	    gap->ga_len = keep;
+	    if (keep >= 1)
+		return stp[keep - 1].st_score;
+	}
     }
     return maxscore;
 }