[BUG] Sending an empty prompt crashes the server

[Lyaaaaaaaaaaaaaaa]

Describe the bug
If the prompt var is empty, the server will crash.

cannot reshape tensor of 0 elements into shape [-1, 0] because the unspecified dimension size -1 can be any value and is ambiguous

To Reproduce
Steps to reproduce the behavior:

1. send an empty prompt to the server

Expected behavior
Shouldn't crash, could return a warning and not generate anything.