`-c sequences=N` suboptimal at N expression cutoff

uglify-js 2.7.5

**actual:**
```
$ echo 'a;b;c;d;e;f;g;h;i;j;k;' | uglifyjs -c sequences=3 -b
```
```
a, b, c;
d;
e, f, g;
h;
i, j, k;
```
**expected**:
```
a, b, c;
d, e, f;
g, h, i;
j, k;
```
Note: should point out that code size in example above is the same, but with real life functions with `if` statements and multiple `return`s it makes a difference.