Array slice overflows (fix #1108)

src/jv.c

@@ -296,10 +296,18 @@ static jv jvp_array_slice(jv a, int start, int end) {
     jv_free(a);
     return jv_array();
   }
-  // FIXME FIXME FIXME large offsets
-  a.offset += start;
-  a.size = end - start;
-  return a;
+
+  if (a.offset + start > 1 << (sizeof(a.offset) * CHAR_BIT)) {
+    jv r = jv_array_sized(end - start);
+    for (int i = start; i < end; i++)
+      r = jv_array_append(r, jv_array_get(jv_copy(a), i));
+    jv_free(a);
+    return r;
+  } else {
+    a.offset += start;
+    a.size = end - start;
+    return a;
+  }
 }
 
 /*