Fix continue! with byebug calls

[deivid-rodriguez]

The continue! command was not ignoring further byebug calls as expected.

Before

$ ruby -r byebug sum.rb 

[1, 9] in /home/deivid/Code/byebug/sum.rb
   1: sum = 0
   2: 
   3: 2.times do |i|
   4:   byebug
=> 5:   sum += i
   6: end
   7: 
   8: byebug
   9: puts "Sum is #{sum}"
(byebug) c!

[1, 9] in /home/deivid/Code/byebug/sum.rb
   1: sum = 0
   2: 
   3: 2.times do |i|
   4:   byebug
=> 5:   sum += i
   6: end
   7: 
   8: byebug
   9: puts "Sum is #{sum}"
(byebug) c!

[1, 9] in /home/deivid/Code/byebug/sum.rb
   1: sum = 0
   2: 
   3: 2.times do |i|
   4:   byebug
   5:   sum += i
   6: end
   7: 
   8: byebug
=> 9: puts "Sum is #{sum}"
(byebug) c!
Sum is 1

After

$ RUBYOPT=-Ilib ruby -r byebug sum.rb 

[1, 9] in /home/deivid/Code/byebug/sum.rb
   1: sum = 0
   2: 
   3: 2.times do |i|
   4:   byebug
=> 5:   sum += i
   6: end
   7: 
   8: byebug
   9: puts "Sum is #{sum}"
(byebug) c!
Sum is 1