libtiff/tif_print.c: TIFFPrintDirectory(): fix null pointer dereference on…

libtiff/tif_print.c: TIFFPrintDirectory(): fix null pointer dereference on corrupted file. Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2770
4 jobs from master in 5 minutes 59 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #46336981
autoconf

05:59

passed #46336982
cmake-makefiles

02:28

passed #46336983
cmake-ninja

02:21

 
  External
passed continuous-integration/appveyor/branch