[HACKERS] standby server crashes hard on out-of-disk-space in HEAD

logfile from a standby server:

2017-06-12 11:43:46.450 EDT [13605] LOG:  started streaming WAL from primary at 3/E6000000 on timeline 1
2017-06-12 11:47:46.992 EDT [11261] FATAL:  could not extend file "base/47578/54806": No space left on device
2017-06-12 11:47:46.992 EDT [11261] HINT:  Check free disk space.
2017-06-12 11:47:46.992 EDT [11261] CONTEXT:  WAL redo at 8/EC7E0CF8 for XLOG/FPI:
2017-06-12 11:47:46.992 EDT [11261] WARNING:  buffer refcount leak: [1243] (rel=base/47578/54806, blockNum=5249,
flags=0x8a000000,refcount=1 1) 
TRAP: FailedAssertion("!(RefCountErrors == 0)", File: "bufmgr.c", Line: 2523)
2017-06-12 11:47:47.567 EDT [11259] LOG:  startup process (PID 11261) was terminated by signal 6: Aborted
2017-06-12 11:47:47.567 EDT [11259] LOG:  terminating any other active server processes
2017-06-12 11:47:47.584 EDT [11259] LOG:  database system is shut down

The FATAL is fine, but we shouldn't have that WARNING I think, and
certainly not the assertion failure.
        regards, tom lane