CVE-2023-54284

In the Linux kernel, the following vulnerability has been resolved:

media: av7110: prevent underflow in writetsto_decoder()

The buf[4] value comes from the user via tsplay(). It is a value in the u8 range. The final length we pass to av7110ipackinstantrepack() is "len - (buf[4] + 1) - 4" so add a check to ensure that the length is not negative. It's not clear that passing a negative len value does anything bad necessarily, but it's not best practice.

With the new bounds checking the "if (!len)" condition is no longer possible or required so remove that.