Fixed SystemStackError

Fix: calling "indirect_rate" method when rates are not defined throws SystemStackError: stack level too deep.

lib/money/bank/russian_central_bank.rb

@@ -24,6 +24,8 @@ def add_rate(from, to, rate)
         super(to, from, 1.0 / rate)
       end
 
+      alias original_get_rate get_rate
+
       def get_rate(from, to)
         update_rates if rates_expired?
         super || indirect_rate(from, to)
@@ -58,7 +60,8 @@ def update_expired_at
       end
 
       def indirect_rate(from, to)
-        get_rate('RUB', to) / get_rate('RUB', from)
+        rate = original_get_rate('RUB', to).to_f / original_get_rate('RUB', from).to_f
+        rate.nan? || !!rate.infinite? ? nil : rate
       end
 
       def local_currencies

spec/lib/money/bank/russian_central_bank_spec.rb

@@ -109,4 +109,14 @@
       end
     end
   end
+
+  describe '#indirect_rate' do
+    before do
+      bank.flush_rates
+    end
+
+    it 'should return nil when indirect rate cannot be calculated' do
+      expect(bank.send(:indirect_rate, 'RUB', 'RUB')).to be_nil
+    end
+  end
 end