patch 8.1.0565: asan complains about reading before allocated block

Problem:    Asan complains about reading before allocated block.
Solution:   Workaround: Avoid offset from becoming negative.

src/gui.c

@@ -2753,7 +2753,8 @@ gui_redraw_block(
 	}
 	else if (enc_utf8)
 	{
-	    if (ScreenLines[off + col1] == 0)
+	    // FIXME: how can the first character ever be zero?
+	    if (col1 > 0 && ScreenLines[off + col1] == 0)
 		--col1;
 # ifdef FEAT_GUI_GTK
 	    if (col2 + 1 < Columns && ScreenLines[off + col2 + 1] == 0)

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    565,
 /**/
     564,
 /**/