patch 8.1.2107: various memory leaks reported by asan

Problem:    Various memory leaks reported by asan.
Solution:   Free the memory. (Ozaki Kiichi, closes #5003)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 159b874..26d8691 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2213,8 +2213,7 @@
 	{
 	    if (rettv_list_alloc(rettv) != FAIL && result != NULL)
 		list_append_string(rettv->vval.v_list, result, -1);
-	    else
-		vim_free(result);
+	    vim_free(result);
 	}
 	else
 	    rettv->vval.v_string = result;