Don't warn when allocating 0 bytes

I was able to reproduce this by starting two computers, and then warming
up the JIT by running:

  while true do os.queueEvent("x") os.pullEvent("x") end

and then running the following on one computer, while typing on the
other:

  while true do end

I'm not quite sure why this happens. It's possible that once the JIT is
warm, we can resume computers without actually allocating anything,
though I'm a little unconvinced.

Fixes #1672

projects/core/src/main/java/dan200/computercraft/core/computer/computerthread/ComputerThread.java

@@ -835,8 +835,8 @@ boolean afterWork() {
                 var allocated = ThreadAllocations.getAllocatedBytes(current) - info.allocatedBytes();
                 if (allocated > 0) {
                     metrics.observe(Metrics.JAVA_ALLOCATION, allocated);
-                } else {
-                    LOG.warn("Allocated a negative number of bytes!");
+                } else if (allocated < 0) {
+                    LOG.warn("Allocated a negative number of bytes ({})!", allocated);
                 }
             }