Blender Git Loki

ImBuf: Add error handling to IMB_indexer_open

Handle return value of `fread()` by printing an error and closing the
file when it cannot be read from. Not only is error handing a good idea,
it also prevents GCC from warning that the return value of `fread()`
should not be ignored:

```
.../blender/source/blender/imbuf/intern/indexer.c: In function ?IMB_indexer_open?:
.../blender/source/blender/imbuf/intern/indexer.c:201:5: warning: ignoring return value of ?fread?, declared with attribute warn_unused_result [-Wunused-result]
201 | fread(&idx->entries[i].frameno, sizeof(int), 1, fp);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../blender/source/blender/imbuf/intern/indexer.c:202:5: warning: ignoring return value of ?fread?, declared with attribute warn_unused_result [-Wunused-result]
202 | fread(&idx->entries[i].seek_pos, sizeof(unsigned long long), 1, fp);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../blender/source/blender/imbuf/intern/indexer.c:203:5: warning: ignoring return value of ?fread?, declared with attribute warn_unused_result [-Wunused-result]
203 | fread(&idx->entries[i].seek_pos_dts, sizeof(unsigned long long), 1, fp);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../blender/source/blender/imbuf/intern/indexer.c:204:5: warning: ignoring return value of ?fread?, declared with attribute warn_unused_result [-Wunused-result]
204 | fread(&idx->entries[i].pts, sizeof(unsigned long long), 1, fp);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Differential Revision: https://developer.blender.org/D9916

Reviewed by: campbellbarton