fix(ida): prevent invalid labels and zero-sized functions

Skip add_func when function size is 0 or negative to avoid
zero-sized function boundaries in IDA.

Skip _miss label when PayloadAddress is 0 (invalid) and _check
label when MonomorphicAddress is shared across many functions,
preventing thousands of labels colliding at the same address.

Tested with obfuscated app: eliminated 5206 set_name(0x0) and
5207 colliding _check labels.