Lua debugger: fix trace command infinite loop.
Lua debugger: fix trace command infinite loop.

Thanks to Itamar Haber for bug report and test case to reproduce.

pedigree/redis,4396/redis,4396/redis,xuguruogu/redis,4396/redis,janekmi/redis,pedigree/redis,pedigree/redis,janekmi/redis,xuguruogu/redis,pedigree/redis,xuguruogu/redis,4396/redis,janekmi/redis,xuguruogu/redis,janekmi/redis