riched20: Add check to ensure iob is a valid index into the object array.

dlls/riched20/richole.c

@@ -1407,7 +1407,7 @@ IRichEditOle_fnGetObject(IRichEditOle *me, LONG iob,
     }
     else
     {
-        if (iob > IRichEditOle_GetObjectCount(me))
+        if (iob < 0 || iob >= IRichEditOle_GetObjectCount(me))
             return E_INVALIDARG;
         LIST_FOR_EACH_ENTRY(reobj, &This->editor->reobj_list, struct re_object, entry)
         {

dlls/riched20/tests/richole.c

@@ -3296,12 +3296,18 @@ static void test_InsertObject(void)
   ok(hr == S_OK, "IRichEditOle_GetObject failed: 0x%08x\n", hr);
   CHECK_REOBJECT_STRUCT(received_reo4, NULL, NULL, reo2.polesite, 2);
 
+  hr = IRichEditOle_GetObject(reole, 3, &received_reo4, REO_GETOBJ_POLESITE);
+  ok(hr == E_INVALIDARG, "IRichEditOle_GetObject should fail: 0x%08x\n", hr);
+
   hr = IRichEditOle_GetObject(reole, 4, &received_reo4, REO_GETOBJ_POLESITE);
   ok(hr == E_INVALIDARG, "IRichEditOle_GetObject should fail: 0x%08x\n", hr);
 
   hr = IRichEditOle_GetObject(reole, 1024, &received_reo4, REO_GETOBJ_POLESITE);
   ok(hr == E_INVALIDARG, "IRichEditOle_GetObject should fail: 0x%08x\n", hr);
 
+  hr = IRichEditOle_GetObject(reole, -10, &received_reo4, REO_GETOBJ_POLESITE);
+  ok(hr == E_INVALIDARG, "IRichEditOle_GetObject should fail: 0x%08x\n", hr);
+
   /* received_reo4 will be zeroed before be used */
   hr = IRichEditOle_GetObject(reole, 2, &received_reo4, REO_GETOBJ_NO_INTERFACES);
   ok(hr == S_OK, "IRichEditOle_GetObject failed: 0x%08x\n", hr);