Fix -Wtautological-overlap-compare in stun test

Fix the minimal check for an invalid IP returned.

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

source/network/tests/test_StunClient.h

@@ -55,7 +55,7 @@ public:
 		{
 			if (c == '.')
 				++dots;
-			else if (c < '0' && c > '9')
+			else if (c < '0' || c > '9')
 			{
 				TS_FAIL("StunClient::FindLocalIP did not return a valid IPV4 address: wrong character");
 				return;