Fix a bug where -DDEBUG would cause an infinite loop in mem_alloc_tiny()
because MEM_ALLOC_SIZE is set to zero (Jumbo-specific) and we ended up
never breaking out of the while loop. Thanks to bytebieger for noticing
the problem and patiently convince me.
Merge branch 'bleeding-jumbo' into memdbg

* bleeding-jumbo:
  Fix a bug where -DDEBUG would cause an infinite loop in mem_alloc_tiny() because MEM_ALLOC_SIZE is set to zero (Jumbo-specific) and we ended up never breaking out of the while loop. Thanks to bytebieger for noticing the problem and patiently convince me.