patch 8.0.0269: may get ml_get error when :perldo deletes lines

Problem:    May get ml_get error when :perldo deletes lines or switches to
            another buffer. (Nikolai Pavlov, issue #1421)
Solution:   Check the buffer and line every time.

src/if_perl.xs

@@ -1286,6 +1286,7 @@ ex_perldo(exarg_T *eap)
     SV		*sv;
     char	*str;
     linenr_T	i;
+    buf_T	*was_curbuf = curbuf;
 
     if (bufempty())
 	return;
@@ -1321,11 +1322,14 @@ ex_perldo(exarg_T *eap)
     SAVETMPS;
     for (i = eap->line1; i <= eap->line2; i++)
     {
+	/* Check the line number, the command my have deleted lines. */
+	if (i > curbuf->b_ml.ml_line_count)
+	    break;
 	sv_setpv(GvSV(PL_defgv), (char *)ml_get(i));
 	PUSHMARK(sp);
 	perl_call_pv("VIM::perldo", G_SCALAR | G_EVAL);
 	str = SvPV(GvSV(PL_errgv), length);
-	if (length)
+	if (length || curbuf != was_curbuf)
 	    break;
 	SPAGAIN;
 	if (SvTRUEx(POPs))

src/testdir/test_perl.vim

@@ -82,6 +82,21 @@ function Test_perldo()
   1
   call assert_false(search('\Cperl'))
   bw!
+
+  " Check deleting lines does not trigger ml_get error.
+  new
+  call setline(1, ['one', 'two', 'three'])
+  perldo VIM::DoCommand("%d_")
+  bwipe!
+
+  " Check switching to another buffer does not trigger ml_get error.
+  new
+  let wincount = winnr('$')
+  call setline(1, ['one', 'two', 'three'])
+  perldo VIM::DoCommand("new")
+  call assert_equal(wincount + 1, winnr('$'))
+  bwipe!
+  bwipe!
 endfunc
 
 function Test_VIM_package()

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    269,
 /**/
     268,
 /**/