patch 8.1.2351: 'wincolor' not used for > for not fitting double width char

Problem:    'wincolor' not used for > for not fitting double width char.
            Also: popup drawn on right half of double width character looks
            wrong.
Solution:   Adjust color for > character.  Clear left half of double width
            character if right half is being overwritten.
diff --git a/src/screen.c b/src/screen.c
index c0f7d49..763d7a8 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -460,6 +460,18 @@
     }
 #endif /* FEAT_RIGHTLEFT */
 
+#ifdef FEAT_TEXT_PROP
+    // First char of a popup window may go on top of the right half of a
+    // double-wide character. Clear the left half to avoid it getting the popup
+    // window background color.
+    if (coloff > 0 && ScreenLines[off_to] == 0)
+    {
+	ScreenLines[off_to - 1] = ' ';
+	ScreenLinesUC[off_to - 1] = 0;
+	screen_char(off_to - 1, row, col + coloff - 1);
+    }
+#endif
+
     redraw_next = char_needs_redraw(off_from, off_to, endcol - col);
 
     while (col < endcol)