Fix flipped pathnavigation.isFlying check

The `!` disappeared as part of the big codegen Lua rewrite

src/navigation/pathnavigator_lua.inl

@@ -28,7 +28,7 @@ namespace {
 [[codegen::luawrap]] bool isFlying() {
     using namespace openspace;
     bool hasFinished = global::navigationHandler->pathNavigator().hasFinished();
-    return hasFinished;
+    return !hasFinished;
 }
 
 // Continue playing a paused camera path.