Fixed #6 Underlocking causing crashes on Android

I fixed this as per the solution in the issue, by surrounding the release
with a try / catch block

src/android/PowerManagement.java

@@ -116,11 +116,16 @@ public class PowerManagement extends CordovaPlugin {
 		PluginResult result = null;
 
 		if( this.wakeLock != null ) {
+			try {
 				this.wakeLock.release();
-			this.wakeLock = null;
-			
 				result = new PluginResult(PluginResult.Status.OK, "OK");
 			}
+			catch (Exception e) {
+				result = new PluginResult(PluginResult.Status.ILLEGAL_ACCESS_EXCEPTION, "WakeLock already released");
+			}
+
+			this.wakeLock = null;
+		}
 		else {
 			result = new PluginResult(PluginResult.Status.ILLEGAL_ACCESS_EXCEPTION, "No WakeLock active - acquire first");
 		}