ivf_video_source.h: fix static analyzer warnings

Check both `feof()` and `ferror()` after `fread()` in `Begin()`, this
prevents warnings in `FillFrame()`:

```
warning: File position of the stream might be 'indeterminate' after a
  failed operation. Can cause undefined behavior [unix.Stream]
warning: Read function called when stream is in EOF state. Function has
  no effect [unix.Stream]
```

Note with `scan-build-19` it is not possible to `ASSERT_EQ/FALSE` both
checks as neither will be interpreted correctly, and execution will be
assumed to be continued. Instead, `ferror()` and `feof()` are manually
checked and an explicit `FAIL()` is used.

Bug: 474642915
Change-Id: Ib6382865452f4cbdaa415d344857984927aec3eb