Conceal Brainfuck in ASCII artwork

Brainhider.rb

#!/usr/bin/env ruby

brainfuck = File.open("helloworld.bf", "rb").read

ascii_art = File.open("animaniacs.art", "rb").read

if brainfuck.length > ascii_art.gsub(" ","").length
	abort "The supplied brainfuck will not fit inside the ASCII art."
end

output = ""
ascii_art.split("").each do |i|
	if brainfuck != ""
		if i != " " and i != "\n"
			i = brainfuck[0,1]
			brainfuck = brainfuck[1..-1]
		end
	end
	output << i
end

File.open( "hidden.bf", "w" ) do |file|
	file.write( output )
end

By only using the >, +, and - characters. if a program finishes running it doesn't need those values anymore, it doesn't generate syntax errors, and it doesn't go out of bounds left. The only thing that can happen is that it goes out of bounds right. It always halts after running those instructions because it doesn't create a loop, and it doesn't freeze because it's never asking for user input. It also doesn't mess up the output because it never prints anything.