[Bug] Wrong index from getCurrentBlockIndex()

### Describe a bug.

**Steps to reproduce:**
1. Create 3 blocks in the following order; 1. Add random text, 2. Keep the second block empty, 3. Add random text on 3rd block
2. For the 3rd block, `getCurrentBlockIndex()` returns wrong index as it skips empty block.

**Expected behavior:**
Should return correct block index regardless of empty blocks inside.

**Device, Browser, OS:**
MacOs

**Editor.js version:**
v2.25.0

This is a serious bug for our use-case, It would be really great to have this fix as soon as possible.