patch 8.0.1561: crash with rust syntax highligting

Problem:    Crash with rust syntax highligting. (Edd Barrett)
Solution:   Avoid going past the end of an empty line.

Author: brammool

src/syntax.c

@@ -2470,7 +2470,8 @@ syn_current_attr(
 
     /* nextgroup ends at end of line, unless "skipnl" or "skipempty" present */
     if (current_next_list != NULL
-	    && syn_getcurline()[current_col + 1] == NUL
+	    && (line = syn_getcurline())[current_col] != NUL
+	    && line[current_col + 1] == NUL
 	    && !(current_next_flags & (HL_SKIPNL | HL_SKIPEMPTY)))
 	current_next_list = NULL;
 

src/version.c

@@ -778,6 +778,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1561,
 /**/
     1560,
 /**/