Fix NEWS-update.jl for cases of empty issues list

Author: timholy

doc/NEWS-update.jl

@@ -5,7 +5,10 @@ NEWS = get(ARGS, 1, "NEWS.md")
 
 s = read(NEWS, String)
 
-s = s[1:match(r"\[#[0-9]+\]:", s).offset-1];
+m = match(r"\[#[0-9]+\]:", s)
+if m !== nothing
+    s = s[1:m.offset-1]
+end
 
 footnote(n) = "[#$n]: https://github.com/JuliaLang/julia/issues/$n"
 N = map(m -> parse(Int,m.captures[1]), eachmatch(r"\[#([0-9]+)\]", s))