Avoid some trouble in non-USD contribution recalc

Don't touch contributions with horribly mangled original_currency,
avoid crashing if no rate can be found.

Change-Id: I3cecd58fe213ed8270f6a6432a4622f81d425191
Merge remote-tracking branch 'origin/master' into deployment

240d5ec Avoid some trouble in non-USD contribution recalc

Change-Id: If88015428290ccac2b6595a2798244511009ec13