Fix boundary condition on resize (#4016)
Fix boundary condition on resize (#4016)

cbuf.size() must be at least one byte larger than cbuf.available() for
logic to work.  reject request to resize = available.
Lan-Hekary/Arduino,lrmoreno007/Arduino,Lan-Hekary/Arduino,Adam5Wu/Arduino,Adam5Wu/Arduino,hallard/Arduino,lrmoreno007/Arduino,Lan-Hekary/Arduino,esp8266/Arduino,hallard/Arduino,sticilface/Arduino,Adam5Wu/Arduino,esp8266/Arduino,hallard/Arduino,sticilface/Arduino,esp8266/Arduino,Lan-Hekary/Arduino,wemos/Arduino,sticilface/Arduino,sticilface/Arduino,wemos/Arduino,lrmoreno007/Arduino,wemos/Arduino,hallard/Arduino,lrmoreno007/Arduino,esp8266/Arduino,wemos/Arduino,lrmoreno007/Arduino,Adam5Wu/Arduino,Lan-Hekary/Arduino,hallard/Arduino,esp8266/Arduino,wemos/Arduino,sticilface/Arduino,Adam5Wu/Arduino