Fix incorrect use of unsafeBuildIncremental in runQueryT

[parenthetical]

A small issue I discovered while writing alternative implementations: runQueryT violates the unsafeBuildIncremental contract. The behavior being sampled only reflects the initial value, not the value at any time:

 runQueryT (QueryT a) qr = do
   ((r, bs), es) <- runReaderT (runEventWriterT (runStateT a mempty)) qr
-  return (r, unsafeBuildIncremental (foldlM (\b c -> (b <>) <$> sample c) mempty bs) (fmapCheap AdditivePatch es))
+  v0 <- foldlM (\b c -> (b <>) <$> sample c) mempty bs
+  inc <- holdIncremental v0 (fmapCheap AdditivePatch es)
+  return (r, inc)

This just happened to work because the unsafe-built incremental tends to be forced immediately.