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)

src/drawline.c

@@ -639,7 +639,7 @@ text_prop_position(
 
     if (wrap || right || above || below || padding > 0 || n_used < *n_extra)
     {
-	int	    col_off = win_col_off(wp) + win_col_off2(wp);
+	int	    col_off = win_col_off(wp) - win_col_off2(wp);
 	int	    skip_add = 0;
 
 	if (above)
@@ -655,7 +655,7 @@ text_prop_position(
 	    if (before < 0
 		    || !(right || below)
 		    || (below
-			? (col_with_padding == 0 || !wp->w_p_wrap)
+			? (col_with_padding <= col_off || !wp->w_p_wrap)
 			: (n_used < *n_extra)))
 	    {
 		if (right && (wrap || room < PROP_TEXT_MIN_CELLS))

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| 

src/testdir/test_textprop.vim

@@ -2653,6 +2653,9 @@ func Test_props_with_text_after_below_trunc()
   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
 

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    718,
 /**/
     717,
 /**/