Fix other bc* function types

Noticed these right after `bcdiv`.
These can both return null if the `modulus` param is 0.

src/Reflection/SignatureMap/functionMap.php

@@ -422,7 +422,7 @@
 'bcadd' => ['string', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
 'bccomp' => ['int', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
 'bcdiv' => ['string|null', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
-'bcmod' => ['string', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
+'bcmod' => ['string|null', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
 'bcmul' => ['string', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],
 'bcompiler_load' => ['bool', 'filename'=>'string'],
 'bcompiler_load_exe' => ['bool', 'filename'=>'string'],
@@ -438,7 +438,7 @@
 'bcompiler_write_header' => ['bool', 'filehandle'=>'resource', 'write_ver='=>'string'],
 'bcompiler_write_included_filename' => ['bool', 'filehandle'=>'resource', 'filename'=>'string'],
 'bcpow' => ['string', 'base'=>'string', 'exponent'=>'string', 'scale='=>'int'],
-'bcpowmod' => ['string', 'base'=>'string', 'exponent'=>'string', 'modulus'=>'string', 'scale='=>'int'],
+'bcpowmod' => ['string|null', 'base'=>'string', 'exponent'=>'string', 'modulus'=>'string', 'scale='=>'int'],
 'bcscale' => ['int', 'scale='=>'int'],
 'bcsqrt' => ['string', 'operand'=>'string', 'scale='=>'int'],
 'bcsub' => ['string', 'left_operand'=>'string', 'right_operand'=>'string', 'scale='=>'int'],