pcal: avoid memory leak when allocation fails

[catenacyber]

Sets PNG_FREE_PCAL as soon as pcal_params is allocated so that even if one of pcal_params[i] allocation fails, the array pcal_params still gets freed by png_free_data

Found by nallocfuzz cf google/oss-fuzz#9902

[catenacyber]

friendly ping @ctruta ?

[ctruta]

friendly ping @ctruta ?

Friendly pong :-)

Apologies for the long wait. I just returned to the project.

Thank you for the discovery and for the fix. I reworked your fix by moving the setting of the PNG_FREE_PCAL flag even earlier than that. I also looked around at the rest of the PNG_FREE_... flags inside that module, and I put them in a more consistent order.

[catenacyber]

Thanks for the better fix :-)