gc: Fix wasDrainNecessary condition

We want to drain when we potentially don't have enough space, not when
there's plenty of space.

Change-Id: I939b3c69764b8b466fa045d0c9ba212722de1329
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/qml/memory/qv4mm.cpp

@@ -707,7 +707,7 @@ static constexpr int markLoopIterationCount = 1024;
 
 bool wasDrainNecessary(MarkStack *ms, QDeadlineTimer deadline)
 {
-    if (ms->remainingBeforeSoftLimit() < markLoopIterationCount)
+    if (ms->remainingBeforeSoftLimit() > markLoopIterationCount)
         return false;
     // drain
     ms->drain(deadline);