Fix for NaN price values.

src/ac/ed/lurg/country/GlobalPrice.java

@@ -95,7 +95,9 @@ public class GlobalPrice implements Serializable {
 				LogWriter.println(String.format("     initally imbalance ratio= %.4f", ratio));
 			}
 			else {
-				if (stockChange >= 0) // stock increasing, so decrease price.  stockChange is positive so adjustment < 1
+				if (stockChange == 0 && production == 0)
+					adjustment=1;
+				else if (stockChange >= 0 && production != 0) // stock increasing, so decrease price.  stockChange is positive so adjustment < 1
 					adjustment = 1 - ModelConfig.MARKET_LAMBA * stockChange/production;
 				else // stock decreasing, so increase price.  stockChange is negative so adjustment > 1
 					adjustment = 1 - ModelConfig.MARKET_LAMBA * stockChange/Math.max(0, stockLevel);