changed DruidDataSource discardConnectiion filling logic

src/main/java/com/alibaba/druid/pool/DruidAbstractDataSource.java

@@ -931,6 +931,10 @@ public abstract class DruidAbstractDataSource extends WrapperAdapter implements
         if (inited && value > this.maxActive) {
             throw new IllegalArgumentException("minIdle greater than maxActive, " + maxActive + " < " + this.minIdle);
         }
+        
+        if (minIdle < 0) {
+            throw new IllegalArgumentException("minIdle must > 0");
+        }
 
         this.minIdle = value;
     }

src/main/java/com/alibaba/druid/pool/DruidDataSource.java

@@ -1059,7 +1059,7 @@ public class DruidDataSource extends DruidAbstractDataSource
             activeCount--;
             discardCount++;
 
-            if (activeCount <= 0) {
+            if (activeCount <= minIdle) {
                 emptySignal();
             }
         } finally {