Fix exception handling (in_sqs.rb)

[JamesJJ]

We found this:

2018-05-10 12:34:59 +0000 [error]: #0 Unexpected error raised. Stopping the timer.
 title=:in_sqs_run_periodic_timer
 error_class=NoMethodError
 error="undefined method `backtrace' for nil:NilClass"

This PR updates the exception handling to prevent exception inside rescue (and so prevent timer being stopped)

Proof of concept in irb:

Before:

$ irb
irb(main):001:0> begin; puts File.join(nil, "hey"); rescue   # Cause some exception
irb(main):002:1> puts $ERROR_INFO.to_s
irb(main):003:1> puts $ERROR_INFO.backtrace
irb(main):004:1> end

NoMethodError: undefined method `backtrace' for nil:NilClass
	from (irb):3:in `rescue in irb_binding'
	from (irb):1
	from /usr/local/bin/irb:11:in `<main>'
irb(main):005:0> ## Exception inside rescue T_T

After:

irb(main):001:0> begin; puts File.join(nil, "hey"); rescue => ex   # Cause some exception
irb(main):002:1> puts ex.to_s
irb(main):003:1> puts ex.backtrace
irb(main):004:1> end
no implicit conversion of nil into String
(irb):1:in `join'
(irb):1:in `irb_binding'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/workspace.rb:87:in `eval'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/workspace.rb:87:in `evaluate'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/context.rb:381:in `evaluate'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:493:in `block (2 levels) in eval_input'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:627:in `signal_status'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:490:in `block in eval_input'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/ruby-lex.rb:246:in `block (2 levels) in each_top_level_statement'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/ruby-lex.rb:232:in `loop'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/ruby-lex.rb:232:in `block in each_top_level_statement'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/ruby-lex.rb:231:in `catch'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb/ruby-lex.rb:231:in `each_top_level_statement'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:489:in `eval_input'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:430:in `block in run'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:429:in `catch'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:429:in `run'
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/irb.rb:385:in `start'
/usr/local/bin/irb:11:in `<main>'
=> nil
irb(main):005:0>  ## Successfully rescued