Fix visual selection w/ ib object

Closes vim#6616

src/testdir/test_textobjects.vim

@@ -41,6 +41,24 @@ func Test_inner_block_with_cpo_M_right_backslash()
   call CpoM('(red (blue\) green)', 1, ['red (blue\) green', 'blue\', 'red (blue\) green'])
 endfunc
 
+func Test_inner_block_single_char()
+  new
+  call setline(1, "(a)")
+
+  set selection=inclusive
+  let @"=''
+  call assert_nobeep('norm! 0faviby')
+  call assert_equal('a', @")
+
+  set selection=exclusive
+  let @"=''
+  call assert_nobeep('norm! 0faviby')
+  call assert_equal('a', @")
+
+  set selection&
+  bwipe!
+endfunc
+
 func Test_quote_selection_selection_exclusive()
   new
   call setline(1, "a 'bcde' f")

src/textobject.c

@@ -1133,8 +1133,10 @@ current_block(
 	/*
 	 * In Visual mode, when the resulting area is not bigger than what we
 	 * started with, extend it to the next block, and then exclude again.
+	 * Don't try to expand the area if the area is empty.
 	 */
 	if (!LT_POS(start_pos, old_start) && !LT_POS(old_end, curwin->w_cursor)
+		&& !EQUAL_POS(start_pos, curwin->w_cursor)
 		&& VIsual_active)
 	{
 	    curwin->w_cursor = old_start;