fix OP_APOST bug for no pre arg cases; fix #2810

src/vm.c

@@ -2125,18 +2125,14 @@ RETRY_TRY_BLOCK:
       int pre  = GETARG_B(i);
       int post = GETARG_C(i);
 
+      struct RArray *ary;
+      int len, idx;
+
       if (!mrb_array_p(v)) {
-        regs[a++] = mrb_ary_new_capa(mrb, 0);
-        while (post--) {
-          SET_NIL_VALUE(regs[a]);
-          a++;
-        }
+        v = mrb_ary_new_from_values(mrb, 1, &regs[a]);
       }
-      else {
-        struct RArray *ary = mrb_ary_ptr(v);
-        int len = ary->len;
-        int idx;
-
+      ary = mrb_ary_ptr(v);
+      len = ary->len;
       if (len > pre + post) {
         regs[a++] = mrb_ary_new_from_values(mrb, len - pre - post, ary->ptr+pre);
         while (post--) {
@@ -2153,7 +2149,6 @@ RETRY_TRY_BLOCK:
           idx++;
         }
       }
-      }
       ARENA_RESTORE(mrb, ai);
       NEXT;
     }