Handle Open3 returning a nil status

Customers are experiencing this in production. It results in an engine
error output of:

    NoMethodError: undefined method `success?' for nil:NilClass
        block in run at /usr/src/app/lib/cc/engine/analyzers/command_line_runner.rb:18

The included spec reproduces this error.

It's unclear what circumstances lead to this, but removing the
NoMethodError will at least let the engine's stderr come through, which
we can then debug and address thereafter.

Author: pbrisbin

lib/cc/engine/analyzers/command_line_runner.rb

@@ -15,10 +15,11 @@ def initialize(command, timeout = DEFAULT_TIMEOUT)
         def run(input)
           Timeout.timeout(timeout) do
             out, err, status = Open3.capture3(command, stdin_data: input)
-            if status.success?
+            if status && status.success?
               yield out
             else
-              raise ::CC::Engine::Analyzers::ParserError, "`#{command}` exited with code #{status.exitstatus}:\n#{err}"
+              exitstatus = status && status.exitstatus
+              raise ::CC::Engine::Analyzers::ParserError, "`#{command}` exited with code #{exitstatus}:\n#{err}"
             end
           end
         end

spec/cc/engine/analyzers/command_line_runner_spec.rb

@@ -26,6 +26,16 @@ module CC::Engine::Analyzers
 
         expect { runner.run("") }.to raise_error(Timeout::Error)
       end
+
+      it "handles Open3 returning a nil status" do
+        runner = CommandLineRunner.new("")
+
+        allow(Open3).to receive(:capture3).and_return(["", "error output", nil])
+
+        expect { runner.run("") }.to raise_error(
+          ParserError, /code :\nerror output/
+        )
+      end
     end
   end
 end