Fix `0:0` locations of warnings

[jubnzv]

When we report a warning in a smart-contract, we should set it location on a contract name instead of 0:0 when possible.

I've seen a few more cases when we report 0:0:

• checker/bad/gold/bad_version.scilla.gold: scilla version missmatch
• checker/bad/gold/bad_init.scilla.gold and checker/bad/gold/extlib_dup_entry.scilla.gold: related to JSON parsing when we don't have locations
• checker/bad/gold/blowup.scilla.gold: insufficient gas error

[anton-trunov]

Thanks! I think those three cases are not very important. Maybe we could do a better job for the Scilla version...