[0.10.x] entities with mineable result of "" crash the game

[Rseding91]

Factorio allows an entity to have a mineable result of "" which crashes the game when you go to mine it.

Steps to reproduce:

• Create a simple entity (container for example)
• Set the mineable result to ""
• Place the entity in-game and mine it

Note the game allows "" for the result but removing result completely throws an error. I would expect it to detect a blank or invalid mineable result and throw an error on load.

[kovarex]

Thank you for the report, this is the way I fixed it:

Fixed setting of minable. Empty result (result="") triggers error message. No result specification makes the entity to have no mining result, but let it be minable.