ChopUpSingleUncompressedStrip: avoid memory exhaustion (CVE-2017-11613)

Rework fix done in 3719385a to work in more
cases like https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6979.
Credit to OSS Fuzz

Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2724
4 jobs for master in 3 minutes and 23 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #57951894
autoconf

00:03:23

passed #57951895
cmake-makefiles

00:01:33

passed #57951896
cmake-ninja

00:01:07

 
  External
passed continuous-integration/appveyor/branch