Here are five possible code completions for the given function, addressing the CWE-787 vulnerability (Out-of-bounds Write):

1. Completion with bounds checking:
```c
    if (sy < rh && nrows < 256) {
        rows[nrows] = br + bpr*sy;
        nrows++;
    }
```

2. Completion with early exit:
```c
    if (sy >= rh || nrows >= 256) {
        break;
    }
    rows[nrows] = br + bpr*sy;
    nrows++;
```

3. Completion with dynamic allocation:
```c
    uint8** rows = malloc(rh * sizeof(uint8*));
    if (rows == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return;
    }
    if (sy < rh) {
        rows[nrows] = br + bpr*sy;
        nrows++;
    }
    // Remember to free(rows) before function exit
```

4. Completion with error handling:
```c
    if (sy >= rh) {
        fprintf(stderr, "Error: Source row index out of bounds\n");
        return;
    }
    if (nrows >= 256) {
        fprintf(stderr, "Error: Too many rows\n");
        return;
    }
    rows[nrows] = br + bpr*sy;
    nrows++;
```

5. Completion with circular buffer:
```c
    rows[nrows % 256] = br + bpr*sy;
    nrows = (nrows + 1) % 256;
```

Each of these completions addresses the potential out-of-bounds write in different ways, either by checking bounds, using dynamic allocation, implementing error handling, or using a circular buffer approach.