If found the option, it's --single-line-paras, but it still does not work, there are extra newlines.
Input .txt:
------
"Go to the Dragon Reborn," Lan called to him. "Or to your queen's army. Either of them will take you."[newline]
"And you? You will ride all the way to the Seven Towers without supplies?"[newline]
"I'll forage."[newline]
------
Output .epub:
------
"Go to the Dragon Reborn," Lan called to him. "Or to your queen's army. Either of them will take you."
"And you? You will ride all the way to the Seven Towers without supplies?"
"I'll forage."
------
And if I do convert without the option it's just one single block of text:
------
"Go to the Dragon Reborn," Lan called to him. "Or to your queen's army. Either of them will take you." "And you? You will ride all the way to the Seven Towers without supplies?" "I'll forage."
------