patch 8.0.1388: char not overwritten with ambiguous width char

Problem:    Char not overwritten with ambiguous width char, if the ambiguous
            char is single width but we reserve double-width space.
Solution:   First clear the screen cells. (Ozaki Kiichi, closes #2436)
diff --git a/src/version.c b/src/version.c
index 2f9957a..b805fd7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1388,
+/**/
     1387,
 /**/
     1386,