Starting rich text with a divider breaks ability for rich text to expand

[kane-knowby]

Steps to Reproduce

1. Create a normal FleatherField
2. Before typing anycharacters, insert a horizontal rule
3. Continue to type as per normal, creating new lines
4. Notice that the text field does not expand

Environment

OS: iOS/Web/Android Flutter version: 3.24 Fleather version: 1.18.0