Parts with VARIANTs have wrong mass in catalog

[lpgagnon]

Moved from KSPModdingLibs/KSPCommunityFixes#93

When a part is configured to have VARIANTs, the parts catalog only takes the VARIANT's mass into account, not the part's own mass field, resulting in too-low masses being reported. Rest of the game correctly(?) adds them up.

Apparently doesn't happen in stock, so RealFuels is the next suspect in line.

@NathanKell re:

@lpgagnon my hunch is that this is an RF bug, since that's what's most likely to be varying the part's mass also using GetModuleMass so if you're bored it'd be awesome if you could double check. Either way though I've confirmed it's not happening on stock Squad parts with partvariants...

Confirmed bug goes away if I just delete RF from my install, but given how much that's going to break (starting with rp1), probably not very meaningful. Did you have a specific kind of double checking in mind?