patch 8.0.1779: deleting in a block selection causes problems

Problem:    Deleting in a block selection causes problems.
Solution:   Check the length of the line before adding bd.textcol and
            bd.textlen. (Christian Brabandt, closes #2825)

Author: brammool

src/ops.c

@@ -2703,6 +2703,8 @@ op_insert(oparg_T *oap, long count1)
     {
 	struct block_def	bd2;
 	int			did_indent = FALSE;
+	size_t			len;
+	int			add;
 
 	/* If indent kicked in, the firstline might have changed
 	 * but only do that, if the indent actually increased. */
@@ -2781,9 +2783,15 @@ op_insert(oparg_T *oap, long count1)
 	 * Subsequent calls to ml_get() flush the firstline data - take a
 	 * copy of the required string.
 	 */
-	firstline = ml_get(oap->start.lnum) + bd.textcol;
+	firstline = ml_get(oap->start.lnum);
+	len = STRLEN(firstline);
+	add = bd.textcol;
 	if (oap->op_type == OP_APPEND)
-	    firstline += bd.textlen;
+	    add += bd.textlen;
+	if ((size_t)add > len)
+	    firstline += len;  // short line, point to the NUL
+	else
+	    firstline += add;
 	if (pre_textlen >= 0
 		     && (ins_len = (long)STRLEN(firstline) - pre_textlen) > 0)
 	{

src/testdir/test_blockedit.vim

@@ -16,5 +16,18 @@ func Test_blockinsert_indent()
   bwipe!
 endfunc
 
+func Test_blockinsert_delete()
+  new
+  let _bs = &bs
+  set bs=2
+  call setline(1, ['case Arg is ', '        when Name_Async,', '        when Name_Num_Gangs,', 'end if;'])
+  exe "norm! ggjVj\<c-v>$o$A\<bs>\<esc>"
+  "call feedkeys("Vj\<c-v>$o$A\<bs>\<esc>", 'ti')
+  call assert_equal(["case Arg is ", "        when Name_Async", "        when Name_Num_Gangs,", "end if;"],
+        \ getline(1,'$'))
+  " reset to sane state
+  let &bs = _bs
+  bwipe!
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1779,
 /**/
     1778,
 /**/