Fix iogate.getc input byte order shuffled bug (#891)

When iogate.cursor_pos is called while handling signal inside iogate.getc, getc return bytes in wrong order.
We need to always check `@buf` after `Reline.core.line_editor.handle_signal` is called.

Author: tompng

lib/reline/io/ansi.rb

@@ -114,13 +114,15 @@ def with_raw_input
   end
 
   def inner_getc(timeout_second)
-    unless @buf.empty?
-      return @buf.shift
-    end
-    until @input.wait_readable(0.01)
+    while true
+      # @buf may change while handling signal, so we need to check it in each loop iteration.
+      return @buf.shift unless @buf.empty?
+      break if @input.wait_readable(0.01)
+
       timeout_second -= 0.01
       return nil if timeout_second <= 0
 
+      # handle_signal may call cursor_pos which modifies @buf
       Reline.core.line_editor.handle_signal
     end
     c = @input.getbyte