patch 9.0.0661: multi-byte "lastline" in 'fillchars' does not work properly

Problem:    Multi-byte "lastline" item in 'fillchars' does not work properly
            when the window is two columns wide.
Solution:   Compute the text length correctly. (closes #11280)
diff --git a/src/drawscreen.c b/src/drawscreen.c
index 3ad7e00..fe54ef5 100644
--- a/src/drawscreen.c
+++ b/src/drawscreen.c
@@ -2643,15 +2643,15 @@
 	{
 	    int		scr_row = W_WINROW(wp) + wp->w_height - 1;
 	    int		symbol  = wp->w_fill_chars.lastline;
-	    int		len;
+	    int		charlen;
 	    char_u	fillbuf[12];  // 2 characters of 6 bytes
 
-	    len =  mb_char2bytes(symbol, &fillbuf[0]);
-	    len += mb_char2bytes(symbol, &fillbuf[len]);
+	    charlen = mb_char2bytes(symbol, &fillbuf[0]);
+	    mb_char2bytes(symbol, &fillbuf[charlen]);
 
 	    // Last line isn't finished: Display "@@@" in the last screen line.
 	    screen_puts_len(fillbuf,
-			    wp->w_width > 2 ? len : wp->w_width,
+			    (wp->w_width > 2 ? 2 : wp->w_width) * charlen,
 			    scr_row, wp->w_wincol, HL_ATTR(HLF_AT));
 	    screen_fill(scr_row, scr_row + 1,
 		    (int)wp->w_wincol + 2, (int)W_ENDCOL(wp),
diff --git a/src/testdir/dumps/Test_display_lastline_6.dump b/src/testdir/dumps/Test_display_lastline_6.dump
new file mode 100644
index 0000000..e5ede7f
--- /dev/null
+++ b/src/testdir/dumps/Test_display_lastline_6.dump
@@ -0,0 +1,10 @@
+>a+0&#ffffff0@1||+1&&|a+0&&@2| @68
+|a| ||+1&&|b+0&&@71
+@2||+1&&|b+0&&@71
+@2||+1&&|b+0&&@55| @15
+|b@1||+1&&|~+0#4040ff13&| @70
+|b+0#0000000&@1||+1&&|~+0#4040ff13&| @70
+|b+0#0000000&@1||+1&&|~+0#4040ff13&| @70
+|@@1||+1#0000000&|~+0#4040ff13&| @70
+|<+3#0000000&|1| |[+1&&|N|o| |N|a|m|e|]| |[|+|]| @40|1|,|1| @11|A|l@1
+|:+0&&|2|v|s|p|l|i|t| @66
diff --git a/src/testdir/dumps/Test_display_lastline_euro_6.dump b/src/testdir/dumps/Test_display_lastline_euro_6.dump
new file mode 100644
index 0000000..80e2cbb
--- /dev/null
+++ b/src/testdir/dumps/Test_display_lastline_euro_6.dump
@@ -0,0 +1,10 @@
+>a+0&#ffffff0@1||+1&&|a+0&&@2| @68
+|a| ||+1&&|b+0&&@71
+@2||+1&&|b+0&&@71
+@2||+1&&|b+0&&@55| @15
+|b@1||+1&&|~+0#4040ff13&| @70
+|b+0#0000000&@1||+1&&|~+0#4040ff13&| @70
+|b+0#0000000&@1||+1&&|~+0#4040ff13&| @70
+|€@1||+1#0000000&|~+0#4040ff13&| @70
+|<+3#0000000&|1| |[+1&&|N|o| |N|a|m|e|]| |[|+|]| @40|1|,|1| @11|A|l@1
+|:+0&&|2|v|s|p|l|i|t| @66
diff --git a/src/testdir/test_display.vim b/src/testdir/test_display.vim
index 4d2ee9f..faed0b5 100644
--- a/src/testdir/test_display.vim
+++ b/src/testdir/test_display.vim
@@ -419,6 +419,10 @@
   call term_sendkeys(buf, ":3split\<CR>")
   call VerifyScreenDump(buf, $'Test_display_lastline_{a:euro}5', {})
 
+  call term_sendkeys(buf, ":close\<CR>")
+  call term_sendkeys(buf, ":2vsplit\<CR>")
+  call VerifyScreenDump(buf, $'Test_display_lastline_{a:euro}6', {})
+
   call StopVimInTerminal(buf)
 endfunc
 
diff --git a/src/version.c b/src/version.c
index 3adb513..e9cc0ec 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    661,
+/**/
     660,
 /**/
     659,