fixes a big with boolean indexing and no elements
fixes a big with boolean indexing and no elements

x[idx] where idx is a boolean array and len(idx)==0 would result in
Swift complaining it could not convert -inf into an int. This patches
that

stsievert/swix,stsievert/swix,scottrhoyt/swix,scottrhoyt/swix,scottsievert/swix,YesVideo/swix,scottrhoyt/swix,YesVideo/swix,scottsievert/swix,YesVideo/swix,YesVideo/swix,scottrhoyt/swix,stsievert/swix,YesVideo/swix,scottsievert/swix,scottsievert/swix,shyamalschandra/swix,scottsievert/swix,YesVideo/swix,scottrhoyt/swix,shyamalschandra/swix,stsievert/swix,stsievert/swix,stsievert/swix,shyamalschandra/swix,scottrhoyt/swix,shyamalschandra/swix,shyamalschandra/swix,scottsievert/swix,shyamalschandra/swix