Errors generating some figures for manual when building current stable

[John W. Eaton]

I'm building

  93f455582f60 (stable)

with a fresh bootstrap and clean build tree on an up-to-date Debian 
testing system using GCC 8.  I am seeing errors like this

  GEN      doc/interpreter/interpft.pdf
warning: division by zero
warning: called from
    legend at line 720 column 14
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 899 column 20
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 990 column 11
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 899 column 20
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 990 column 11
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 899 column 20
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 990 column 11
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 909 column 20
    interpimages at line 43 column 5
warning: division by zero
warning: called from
    legend at line 990 column 11
    interpimages at line 43 column 5
Error: /undefined in -nan
Operand stack:
   --nostringval--   (0)   --nostringval--   0
Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval-- 
--nostringval--   2   %stopped_push   --nostringval--   --nostringval-- 
 --nostringval--   false   1   %stopped_push   1990   1   3 
%oparray_pop   1989   1   3   %oparray_pop   1988   1   3   %oparray_pop 
  --nostringval--   1977   1   3   %oparray_pop   1833   1   3 
%oparray_pop   --nostringval--   %errorexec_pop   .runexec2 
--nostringval--   --nostringval--   --nostringval--   2   %stopped_push 
 --nostringval--
Dictionary stack:
   --dict:733/1123(ro)(G)--   --dict:0/20(G)--   --dict:80/200(L)-- 
--dict:42/64(L)--
Current allocation mode is local
GPL Ghostscript 9.50: Unrecoverable error, exit code 1


These problems appear to be repeatable.  It doesn't affect all the 
figures.  I don't recall seeing these before.  Is it just me, or is 
anyone else seeing these problems?

jwe