patch 9.0.0116: virtual text not displayed if 'signcolumn' is "yes"

Problem:    Virtual text not displayed if 'signcolumn' is "yes".
Solution:   Set c_extra and c_final to NUL.
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index 6630143..5a3f9b3 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -2204,7 +2204,10 @@
   END
   call writefile(lines, 'XscriptPropsWithText')
   let buf = RunVimInTerminal('-S XscriptPropsWithText', #{rows: 6, cols: 60})
-  call VerifyScreenDump(buf, 'Test_prop_inserts_text', {})
+  call VerifyScreenDump(buf, 'Test_prop_inserts_text_1', {})
+
+  call term_sendkeys(buf, ":set signcolumn=yes\<CR>")
+  call VerifyScreenDump(buf, 'Test_prop_inserts_text_2', {})
 
   call StopVimInTerminal(buf)
   call delete('XscriptPropsWithText')