patch 9.0.0718: extra empty line between two virtual text "below"

Problem:    Extra empty line between two virtual text "below" when 'wrap' and
            'number' are set.
Solution:   Reset "before" when there is no text in the screen line.
            (closes #11334)
diff --git a/src/testdir/dumps/Test_prop_with_text_after_below_trunc_2.dump b/src/testdir/dumps/Test_prop_with_text_after_below_trunc_2.dump
new file mode 100644
index 0000000..1d93f9f
--- /dev/null
+++ b/src/testdir/dumps/Test_prop_with_text_after_below_trunc_2.dump
@@ -0,0 +1,8 @@
+| +0#af5f00255#ffffff0@1|1| |o+0#0000000&|n|a|s|d|f| |a|s|d|f| |a|s|d|f| |a|s|d|f| |a|s|d| |f|a|s| |d|f|t+0#e000e06&|h|e| |q|u|i|c|k| |b|r|o|w|n| |f|o|x| |j|u|m|…
+| +0#af5f00255&@3|t+0#e000e06&|h|e| |q|u|i|c|k| |b|r|o|w|n| |f|o|x| |j|u|m|p|s| |o|v|e|r| |t|h|e| |l|a|z|y| |d|o|g| +0#0000000&@12
+| +0#af5f00255&@1|2| |t+0#0000000&|w>o| @52
+|~+0#4040ff13&| @58
+|~| @58
+|~| @58
+|~| @58
+|:+0#0000000&|s|e|t| |n|u|m|b|e|r| @30|2|,|3| @10|A|l@1| 
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index b4178e5..3fb27c9 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -2653,6 +2653,9 @@
   let buf = RunVimInTerminal('-S XscriptPropsAfterTrunc', #{rows: 8, cols: 60})
   call VerifyScreenDump(buf, 'Test_prop_with_text_after_below_trunc_1', {})
 
+  call term_sendkeys(buf, ":set number\<CR>")
+  call VerifyScreenDump(buf, 'Test_prop_with_text_after_below_trunc_2', {})
+
   call StopVimInTerminal(buf)
 endfunc