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)

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1388,
 /**/
     1387,
 /**/