Do not try to use miniupnp if upnp support is disabled

build/CMakeLists.txt

@@ -247,11 +247,9 @@ if(NOT DEFINED OPENSSL_INCLUDE_DIR)
   message(SEND_ERROR "Could not find OpenSSL. Please download and install it first!")
 endif()
 
-find_package ( MiniUPnPc )
-if (MINIUPNPC_FOUND)
-  include_directories( ${MINIUPNPC_INCLUDE_DIR} )
-else ()
-  set(WITH_UPNP OFF)
+if (WITH_UPNP)
+  find_package ( MiniUPnPc REQUIRED )
+  include_directories( SYSTEM ${MINIUPNPC_INCLUDE_DIR} )
 endif()
 
 find_package ( ZLIB )