Fix tcache crash during thread cleanup.
Fix tcache crash during thread cleanup.

Properly maintain tcache_bin_t's avail pointer such that it is NULL if
no objects are cached.  This only caused problems during thread cache
destruction, since cache flushing otherwise never occurs on an empty
bin.

geekboxzone/mmallow_external_jemalloc,Snaipe/jemalloc,CyanogenMod/android_external_jemalloc,TeamExodus/external_jemalloc,wqfish/jemalloc,percona/jemalloc-debian,jemalloc/jemalloc-cmake,VRToxin/android_external_jemalloc,8l/jemalloc,CMRemix/android_external_jemalloc,flyfeifan/jemalloc,VRToxin/android_external_jemalloc,CMRemix/android_external_jemalloc,sudosurootdev/external_jemalloc,dcreager/jemalloc,tempbottle/jemalloc,vashstorm/jemalloc,jemalloc/jemalloc-cmake,glandium/jemalloc,shekkbuilder/jemalloc,wfxiang08/jemalloc,wfxiang08/jemalloc,sudosurootdev/external_jemalloc,vashstorm/jemalloc,garoose/jemalloc,flyfeifan/jemalloc,VRToxin/android_external_jemalloc,TeamExodus/external_jemalloc,wqfish/jemalloc,android-ia/platform_external_jemalloc,dcreager/jemalloc,xin3liang/platform_external_jemalloc,wfxiang08/jemalloc,garoose/jemalloc,Dmitry-Me/jemalloc,tempbottle/jemalloc,yy-nm/jemalloc,Dmitry-Me/jemalloc,lvfeng1130/jemalloc,android-ia/platform_external_jemalloc,awreece/jemalloc,lilothar/jemalloc,geekboxzone/lollipop_external_jemalloc,flyfeifan/jemalloc,xin3liang/platform_external_jemalloc,AndroidExternal/jemalloc,kmiku7/jemalloc,vashstorm/jemalloc,wqfish/jemalloc,wespelee/jemalloc,yy-nm/jemalloc,dxq-git/jemalloc,percona/jemalloc-debian,flyfeifan/jemalloc,Dmitry-Me/jemalloc,dxq-git/jemalloc,wespelee/jemalloc,lvfeng1130/jemalloc,AndroidExternal/jemalloc,awreece/jemalloc,garoose/jemalloc,jemalloc/jemalloc-cmake,ahmetmircik/jemalloc,cpeterso/jemalloc,garoose/jemalloc,CyanogenMod/android_external_jemalloc,8l/jemalloc,leebaok/jemalloc-4.2.1-readcode,geekboxzone/lollipop_external_jemalloc,wqfish/jemalloc,CMRemix/android_external_jemalloc,AndroidExternal/jemalloc,geekboxzone/mmallow_external_jemalloc,geekboxzone/mmallow_external_jemalloc,leebaok/jemalloc-4.2.1-readcode,ahmetmircik/jemalloc,wqfish/jemalloc,percona/jemalloc-debian,shekkbuilder/jemalloc,ahmetmircik/jemalloc,TeamExodus/external_jemalloc,CMRemix/android_external_jemalloc,VRToxin/android_external_jemalloc,glandium/jemalloc,lvfeng1130/jemalloc,geekboxzone/mmallow_external_jemalloc,xin3liang/platform_external_jemalloc,wfxiang08/jemalloc,percona/jemalloc-debian,geekboxzone/lollipop_external_jemalloc,jemalloc/jemalloc-cmake,awreece/jemalloc,vashstorm/jemalloc,glandium/jemalloc,wespelee/jemalloc,android-ia/platform_external_jemalloc,yy-nm/jemalloc,CyanogenMod/android_external_jemalloc,geekboxzone/lollipop_external_jemalloc,8l/jemalloc,dxq-git/jemalloc,kmiku7/jemalloc,Snaipe/jemalloc,kmiku7/jemalloc,AndroidExternal/jemalloc,dxq-git/jemalloc,wespelee/jemalloc,splbio/jemalloc,lilothar/jemalloc,splbio/jemalloc,kmiku7/jemalloc,Snaipe/jemalloc,shekkbuilder/jemalloc,android-ia/platform_external_jemalloc,Snaipe/jemalloc,splbio/jemalloc,leebaok/jemalloc-4.2.1-readcode,lilothar/jemalloc,Dmitry-Me/jemalloc,TeamExodus/external_jemalloc,yy-nm/jemalloc,leebaok/jemalloc-4.2.1-readcode,awreece/jemalloc,sudosurootdev/external_jemalloc,lilothar/jemalloc,ahmetmircik/jemalloc,cpeterso/jemalloc,cpeterso/jemalloc,glandium/jemalloc,dcreager/jemalloc,lvfeng1130/jemalloc,sudosurootdev/external_jemalloc,8l/jemalloc,xin3liang/platform_external_jemalloc,tempbottle/jemalloc,shekkbuilder/jemalloc,tempbottle/jemalloc,CyanogenMod/android_external_jemalloc,cpeterso/jemalloc