Attempt to read property "is_block_editor" on null in loader.php

### Describe the bug:
PHP Warning: Attempt to read property "is_block_editor" on null in /coblocks/includes/block-migrate/loader.php on line 35

### To reproduce:
Try to edit an Elementor Landing page with CoBlocks enabled. Probably not limited to just Elementor Landing Pages. The warning shows up in the error logs afterwards.

### Expected behavior:
Not to have errors

### Screenshots:
It's in the error logs, no screenshot available

### Isolating the problem:
It's due to poor error handling. The 'the_post' action does check if the get_current_screen function exists, but it doesn't check if it's null or not an object before using.

```
if (!is_admin() || !get_current_screen()->is_block_editor) {
return;
}
```
It should be something like this:
```
$current_screen = get_current_screen();
if (!is_admin() || ($current_screen && method_exists( $current_screen, 'is_block_editor' ) && !$current_screen->is_block_editor)) {
return;
}
```

### WordPress version:
6.3.2

### Gutenberg version:
N/A

Elementor version: 3.16.6
Elementor Pro version: 3.16.2
Coblocks version: 3.1.4