reraise IOError on yield of io, when the error doesn't involve the

client io specifically.

This was the case for multipart tests raising IOErrors on upload files
instead of IO, which was causing the loop to break.

lib/httpx/selector.rb

@@ -117,6 +117,7 @@ class HTTPX::Selector
     yield io
   rescue IOError, SystemCallError
     @selectables.reject!(&:closed?)
+    raise unless @selectables.empty?
   end
 
   def select(interval, &block)