Fix precision of average_output_time

The fix as suggested by <jberman> on IRC. Before the fix, it would truncate 1.9 to 1 skewing the output selection.

src/wallet/wallet2.cpp

@@ -1031,7 +1031,7 @@ gamma_picker::gamma_picker(const std::vector<uint64_t> &rct_offsets, double shap
   end = rct_offsets.data() + rct_offsets.size() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE;
   num_rct_outputs = *(end - 1);
   THROW_WALLET_EXCEPTION_IF(num_rct_outputs == 0, error::wallet_internal_error, "No rct outputs");
-  average_output_time = DIFFICULTY_TARGET_V2 * blocks_to_consider / outputs_to_consider; // this assumes constant target over the whole rct range
+  average_output_time = DIFFICULTY_TARGET_V2 * blocks_to_consider / static_cast<double>(outputs_to_consider); // this assumes constant target over the whole rct range
 };
 
 gamma_picker::gamma_picker(const std::vector<uint64_t> &rct_offsets): gamma_picker(rct_offsets, GAMMA_SHAPE, GAMMA_SCALE) {}