fix #H7980 - multiple weapon attacks when poly'd

fix #H7980 - multiple weapon attacks when poly'd

This fixes the weapon related aspects of #H7980:  having an alternate
weapon be used in cases where it shouldn't when polymorphed into a
monster form with multiple weapon attacks.  The most egregious was
using an off-hand artifact, but it would also use off-hand two-handed
weapon, off-hand silver weapon when in silver-hating form, or any
reasonable off-hand weapon when wearing a shield.  That last is iffy
whether or not to allow, since you'll still get the extra attacks
whether it switches to secondary weapon or stays with the primary.
I've made it re-use the primary since two-weapon mode doesn't allow
a shield.  The other oddity was being able to use the secondary
weapon on the second swing even if the first swing was weaponless.
I went with ingoring the secondary weapon if there's no primary one
or if the primary is two-handed.

Report included "cursed secondary doesn't weld" but that has nothing
to do with polymorph attacking.  I've changed that to drop the weapon
if you attack with it when it's cursed, similar to what happens when
secondary weapon becomes cursed while two-weaponing.

It also included "marilith's attacks beyond the second don't use any
weapon and can hit cockatrices without touching them".  A marilith has
two weapon attacks and then four claw attacks.  Claw attacks only use
the weapon if it hasn't been used yet, so marilith hits with primary,
secondary (or primary a second time if no secondary), claw, claw,
claw, claw and that's the intended behavior.  It is able to hit
cockatrices if wielding anything at all, same as a monster with just
a single attack.  Since it is impossible to wield six weapons or three
pairs of gloves, that has to be intended behavior too.  Playability
trumps realism even if it is silly to hit without a 3rd through 6th
weapon and be safe from touching the target due to the 1st weapon or
one pair of gloves.  [Situation is different from having no control
over unsafely biting something after making a safe weapon or claw
attack; perhaps a better solution would be to refrain from using the
four claw attacks when attacking something that is fatal to touch.]