To generate the patch for the given code slice, we need to follow a structured approach to identify the root cause of the vulnerability and then apply an appropriate fix. Here are the detailed reasoning steps:

### Step 1: Root Cause Analysis

1. **Understanding the Code Context:**
   - The function `hevc_parse_slice_segment` is parsing a slice segment from a bitstream.
   - `pps_id` is read from the bitstream using the function `gf_bs_read_ue_log`.
   - `pps_id` is then used as an index to access the `pps` array in the `hevc` structure.

2. **Identifying the Vulnerability:**
   - The line `pps = &hevc->pps[pps_id];` accesses the `pps` array using `pps_id`.
   - The array `hevc->pps` has a fixed size of 64 elements.
   - The current check `if (pps_id >= 64)` ensures that `pps_id` is not greater than or equal to 64.
   - However, there is no check to ensure that `pps_id` is non-negative.

3. **Potential Vulnerability:**
   - If `pps_id` is negative, the expression `hevc->pps[pps_id]` will result in an out-of-bounds access.
   - This can lead to reading or writing memory outside the bounds of the `pps` array, causing undefined behavior and potential security issues.

### Step 2: Fixing Strategy

1. **Ensuring Valid Index Range:**
   - To prevent out-of-bounds access, we need to ensure that `pps_id` is within the valid range of the array indices.
   - The valid range for `pps_id` should be from 0 to 63 (inclusive).

2. **Adding the Missing Check:**
   - The current check only ensures that `pps_id` is less than 64.
   - We need to add an additional check to ensure that `pps_id` is non-negative.

3. **Implementing the Fix:**
   - Modify the condition to check both the lower and upper bounds of `pps_id`.
   - The updated condition should be `if ((pps_id < 0) || (pps_id >= 64))`.

### Conclusion

The root cause of the vulnerability is the lack of a check to ensure that `pps_id` is non-negative. The fix involves adding this missing check to ensure that `pps_id` is within the valid range of array indices. The patch is as follows:

```diff
< 	if (pps_id >= 64)
---
> 	if ((pps_id < 0) || (pps_id >= 64))
```

This patch ensures that `pps_id` is both non-negative and less than 64, thereby preventing out-of-bounds access to the `pps` array and mitigating the CWE-125 vulnerability.