patch 8.2.5008: when 'formatoptions' contains "/" wrongly wrapping comment

Problem:    When 'formatoptions' contains "/" wrongly wrapping a long trailing
            comment.
Solution:   Pass the OPENLINE_FORMAT flag.

src/testdir/test_textformat.vim

@@ -289,11 +289,28 @@ func Test_format_c_comment()
       x
   END
   call assert_equal(expected, getline(1, '$'))
+
+  " Comment is formatted when it wraps
+  normal 2GA with some more text added
+  let expected =<< trim END
+      nop;
+      val = val;      // This is a comment
+                      // with some more text
+                      // added
+      x
+  END
+  call assert_equal(expected, getline(1, '$'))
+
   set fo-=/
 
   " using 'indentexpr' instead of 'cindent' does not repeat a comment
   setl nocindent indentexpr=2
-  3delete
+  %del
+  let text =<< trim END
+      nop;
+      val = val;      // This is a comment
+  END
+  call setline(1, text)
   normal 2Gox
   let expected =<< trim END
       nop;