Fix NULL pointer dereference in webadmin.

https://github.com/znc/znc/commit/2bd410ee5570cea127233f1133ea22f25174eb28
--- modules/webadmin.cpp
+++ modules/webadmin.cpp
@@ -404,7 +426,7 @@
 			CIRCNetwork* pNetwork = SafeGetNetworkFromParam(WebSock);
 
 			// Admin||Self Check
-			if (!spSession->IsAdmin() && (!spSession->GetUser() || spSession->GetUser() != pNetwork->GetUser())) {
+			if (!spSession->IsAdmin() && (!spSession->GetUser() || !pNetwork || spSession->GetUser() != pNetwork->GetUser())) {
 				return false;
 			}
 
@@ -433,7 +455,7 @@
 			CIRCNetwork* pNetwork = SafeGetNetworkFromParam(WebSock);
 
 			// Admin||Self Check
-			if (!spSession->IsAdmin() && (!spSession->GetUser() || spSession->GetUser() != pNetwork->GetUser())) {
+			if (!spSession->IsAdmin() && (!spSession->GetUser() || !pNetwork || spSession->GetUser() != pNetwork->GetUser())) {
 				return false;
 			}
 
@@ -457,7 +479,7 @@
 			CIRCNetwork* pNetwork = SafeGetNetworkFromParam(WebSock);
 
 			// Admin||Self Check
-			if (!spSession->IsAdmin() && (!spSession->GetUser() || spSession->GetUser() != pNetwork->GetUser())) {
+			if (!spSession->IsAdmin() && (!spSession->GetUser() || !pNetwork || spSession->GetUser() != pNetwork->GetUser())) {
 				return false;
 			}
 
@@ -471,7 +493,7 @@
 			CIRCNetwork* pNetwork = SafeGetNetworkFromParam(WebSock);
 
 			// Admin||Self Check
-			if (!spSession->IsAdmin() && (!spSession->GetUser() || spSession->GetUser() != pNetwork->GetUser())) {
+			if (!spSession->IsAdmin() && (!spSession->GetUser() || !pNetwork || spSession->GetUser() != pNetwork->GetUser())) {
 				return false;
 			}