fix github issue #907 - bad shade logic

Issue reported by vultur-cadens:  one of the checks for whether a
shade would be harmed by an attack was erroneously inside a block
of code that only executed when you could see the attack.  Basic
physical damage wasn't affected but some monster (or poly'd hero)
damage types that shouldn't affect shades didn't when seen but did
when unseen.

Could also get "attack passes harmlessly through the shade" when
an unseen attack for physical damage hit and failed to deal damage.

fixes #907

doc/fixes3-7-0.txt

@@ -1048,6 +1048,8 @@ guardian nagas' constriction attack could never hit because the two preceding
 	attacks must both hit and those were mutually exclusive: bite and spit
 explicitly throwing 1 for non-gold stack of more than 1 and then canceling at
 	direction prompt left a pair of stacks of 1 and N-1 with same invlet
+some attack damage which shouldn't affect shades operated as intended when
+	hero could see it happen but erroneously affected them when not seen
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository