Improve implementation of viable?.

Author: ioquatix

lib/async/http/protocol/http1/connection.rb

@@ -52,7 +52,7 @@ def concurrency
 
 					# Can we use this connection to make requests?
 					def viable?
-						@ready && !@stream.closed? && @stream&.readable?
+						@ready && @stream && !@stream.closed? && @stream.readable?
 					end
 
 					def reusable?

lib/async/http/protocol/http2/connection.rb

@@ -129,7 +129,7 @@ def concurrency
 
 					# Can we use this connection to make requests?
 					def viable?
-						!@stream.closed? && @stream.readable?
+						@stream && !@stream.closed? && @stream.readable?
 					end
 
 					def reusable?