[ruby/irb] Change StdioInputMethod#eof? to non-blocking

This fixes --inf-ruby-mode.

https://github.com/ruby/irb/commit/0e4a818955

lib/irb/input-method.rb

@@ -83,7 +83,15 @@ module IRB
     #
     # See IO#eof? for more information.
     def eof?
-      @stdin.eof?
+      rs, = IO.select([@stdin], [], [], 0.00001)
+      if rs and rs[0]
+        c = @stdin.getc
+        result = c.nil? ? true : false
+        @stdin.ungetc(c) unless c.nil?
+        result
+      else # buffer is empty
+        false
+      end
     end
 
     # Whether this input method is still readable when there is no more data to