Nested `for` loops - Broken iteration

# Overview
The following code snippet produces the wrong result:
```zig
for (0..5) |i| {
    for (0..3) |j| {
        @println(i, j);
    }
}
```

## Expected Output
```
00
01
02
10
11
12
20
21
22
30
31
32
40
41
42
```

## Actual Output
```
00
01
02
10
11
12
20
21
22
```