Move the cursor correctly when deleting at eol

This fixes #246.

Author: aycabta

lib/reline/line_editor.rb

@@ -2395,6 +2395,9 @@ def finish
       width = Reline::Unicode.get_mbchar_width(mbchar)
       @cursor_max -= width
       if @cursor > 0 and @cursor >= @cursor_max
+        byte_size = Reline::Unicode.get_prev_mbchar_size(@line, @byte_pointer)
+        mbchar = @line.byteslice(@byte_pointer - byte_size, byte_size)
+        width = Reline::Unicode.get_mbchar_width(mbchar)
         @byte_pointer -= byte_size
         @cursor -= width
       end

test/reline/test_key_actor_vi.rb

@@ -1434,4 +1434,22 @@ def test_pasting_fullwidth
     assert_cursor(4)
     assert_cursor_max(4)
   end
+
+  def test_ed_delete_next_char_at_eol
+    input_keys('"あ"')
+    assert_line('"あ"')
+    assert_byte_pointer_size('"あ"')
+    assert_cursor(4)
+    assert_cursor_max(4)
+    input_keys("\C-[")
+    assert_line('"あ"')
+    assert_byte_pointer_size('"あ')
+    assert_cursor(3)
+    assert_cursor_max(4)
+    input_keys('xa"')
+    assert_line('"あ"')
+    assert_byte_pointer_size('"あ"')
+    assert_cursor(4)
+    assert_cursor_max(4)
+  end
 end