clang: suppress a warning

    lib/db.c:3098:7: warning: initializing 'int *'
          with an expression of type 'uint32_t *' (aka 'unsigned int *') converts
          between pointers to integer types with different sign [-Wpointer-sign]
          GRN_TABLE_EACH(ctx, table2, 0, 0, id, &key, &key_size, &value2, {
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It seems that we should treat all key sizes as unsigned int.

include/groonga.h

@@ -3008,10 +3008,11 @@ GRN_API grn_rc grn_dat_cursor_delete(grn_ctx *ctx, grn_dat_cursor *c,
   grn_dat_cursor *_sc = grn_dat_cursor_open(ctx, dat, NULL, 0, NULL, 0, 0, -1, 0);\
   if (_sc) {\
     grn_id id;\
-    int *_ks = (key_size);\
+    unsigned int *_ks = (key_size);\
     if (_ks) {\
       while ((id = grn_dat_cursor_next(ctx, _sc))) {\
-        *(_ks) = grn_dat_cursor_get_key(ctx, _sc, (const void **)(key));\
+        int _ks_raw = grn_dat_cursor_get_key(ctx, _sc, (const void **)(key));\
+        *(_ks) = (unsigned int)_ks_raw;\
         block\
       }\
     } else {\