[PATCH] DAC960 fix for NULL dereference in open()

This fixes a problem that's been hidden for a while.

DAC960_open() will try to dereference a NULL pointer if an application
opens (for example) /dev/rd/c0d12 when there has never been a logical
device created for that file.

drivers/block/DAC960.c

@@ -82,7 +82,7 @@ static int DAC960_open(struct inode *inode, struct file *file)
 	} else {
 		DAC960_V2_LogicalDeviceInfo_T *i =
 			p->V2.LogicalDeviceInformation[drive_nr];
-		if (i->LogicalDeviceState == DAC960_V2_LogicalDevice_Offline)
+		if (!i || i->LogicalDeviceState == DAC960_V2_LogicalDevice_Offline)
 			return -ENXIO;
 	}