Fix for ENG-998. If there is no thread pool do the work in the selection thread.
Fix for ENG-998. If there is no thread pool do the work in the selection thread.

VoltDB/voltdb,flybird119/voltdb,ingted/voltdb,ingted/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,wolffcm/voltdb,flybird119/voltdb,paulmartel/voltdb,creative-quant/voltdb,kobronson/cs-voltdb,simonzhangsm/voltdb,wolffcm/voltdb,deerwalk/voltdb,kumarrus/voltdb,creative-quant/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,flybird119/voltdb,creative-quant/voltdb,wolffcm/voltdb,ingted/voltdb,migue/voltdb,simonzhangsm/voltdb,deerwalk/voltdb,kobronson/cs-voltdb,flybird119/voltdb,creative-quant/voltdb,flybird119/voltdb,kumarrus/voltdb,zuowang/voltdb,kobronson/cs-voltdb,migue/voltdb,deerwalk/voltdb,wolffcm/voltdb,zuowang/voltdb,flybird119/voltdb,simonzhangsm/voltdb,paulmartel/voltdb,wolffcm/voltdb,paulmartel/voltdb,simonzhangsm/voltdb,migue/voltdb,VoltDB/voltdb,zuowang/voltdb,kumarrus/voltdb,deerwalk/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,kumarrus/voltdb,zuowang/voltdb,VoltDB/voltdb,wolffcm/voltdb,migue/voltdb,zuowang/voltdb,zuowang/voltdb,creative-quant/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,flybird119/voltdb,flybird119/voltdb,kobronson/cs-voltdb,ingted/voltdb,ingted/voltdb,creative-quant/voltdb,kobronson/cs-voltdb,kumarrus/voltdb,deerwalk/voltdb,zuowang/voltdb,creative-quant/voltdb,kumarrus/voltdb,creative-quant/voltdb,simonzhangsm/voltdb,migue/voltdb,ingted/voltdb,migue/voltdb,kumarrus/voltdb,ingted/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,deerwalk/voltdb,migue/voltdb,kumarrus/voltdb,deerwalk/voltdb,paulmartel/voltdb,zuowang/voltdb,VoltDB/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,migue/voltdb,wolffcm/voltdb,wolffcm/voltdb,deerwalk/voltdb,ingted/voltdb,paulmartel/voltdb