patch 8.2.2508: cannot change the character displayed in non existing lines

Problem:    Cannot change the character displayed in non existing lines.
Solution:   Add the "eob" item to 'fillchars'. (closes #7832, closes #3820)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index ee5ee26..08d205c 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3235,7 +3235,7 @@
 	Only normal file name characters can be used, "/\*?[|<>" are illegal.
 
 						*'fillchars'* *'fcs'*
-'fillchars' 'fcs'	string	(default "vert:|,fold:-")
+'fillchars' 'fcs'	string	(default "vert:|,fold:-,eob:~")
 			global
 			{not available when compiled without the |+folding|
 			feature}
@@ -3248,6 +3248,7 @@
 	  vert:c	'|'		vertical separators |:vsplit|
 	  fold:c	'-'		filling 'foldtext'
 	  diff:c	'-'		deleted lines of the 'diff' option
+	  eob:c		'~'		empty lines below the end of a buffer
 
 	Any one that is omitted will fall back to the default.  For "stl" and
 	"stlnc" the space will be used when there is highlighting, '^' or '='
@@ -3267,6 +3268,7 @@
 	  vert:c	VertSplit		|hl-VertSplit|
 	  fold:c	Folded			|hl-Folded|
 	  diff:c	DiffDelete		|hl-DiffDelete|
+	  eob:c		EndOfBuffer		|hl-EndOfBuffer|
 
 		*'fixendofline'* *'fixeol'* *'nofixendofline'* *'nofixeol'*
 'fixendofline' 'fixeol'	boolean	(default on)