WifiNanIface: Validate interface before cleanup.

Calling invalidate() API twice would lead to fatal error. This
commit is to check if interface isValid() before doing other operations
in invalidate() API.

Bug: 166412651
Test: atest VtsHalWifiNanV1_4TargetTest WifiNanIfaceTest
Change-Id: Ia3fc48bb3d98660705bba9a32b7a5845ff7af79f
diff --git a/wifi/1.4/default/wifi_nan_iface.cpp b/wifi/1.4/default/wifi_nan_iface.cpp
index 5764d35..24ffb17 100644
--- a/wifi/1.4/default/wifi_nan_iface.cpp
+++ b/wifi/1.4/default/wifi_nan_iface.cpp
@@ -534,6 +534,9 @@
 }
 
 void WifiNanIface::invalidate() {
+    if (!isValid()) {
+        return;
+    }
     // send commands to HAL to actually disable and destroy interfaces
     legacy_hal_.lock()->nanDisableRequest(ifname_, 0xFFFF);
     legacy_hal_.lock()->nanDataInterfaceDelete(ifname_, 0xFFFE, "aware_data0");