Address issue #1539 - infinite loop in peg split

Other looping rules ensure forward progress by terminating if an
iteration is at the same location as the previous iteration. Do the same
for split.

test/suite-peg.janet

@@ -772,5 +772,16 @@
   "5:apple6:banana6:cherry"
   @["apple" "banana" "cherry"])
 
+# Issue #1539 - make sure split with "" doesn't infinite loop/oom
+(test "issue 1539"
+      ~(split "" (capture (to -1)))
+      "hello there friends"
+      nil)
+
+(test "issue 1539 pt. 2"
+  ~(split "," (capture 0))
+  "abc123,,,,"
+  @["" "" "" "" ""])
+
 (end-suite)