fit now segfaults

[sfeam <sf...@us...>]

Unfortunately, since yesterday's change to fit.c I get a segfault
from the fit demo:

gnuplot> load 'fit.dem'
Some examples how data fitting using nonlinear least squares fit can be done.

We fit a straight line to the data -- only as a demo without physical meaning.
  fit function:l(x) = y0 + m*x
  initial parameters: y0 = 0, m = 0
  fit command: fit l(x) 'lcdemo.dat' via y0, m

Now start fitting...  (-> return)
fit: Deprecated syntax. Consider using the 'noerror' option, see `help fit`.

Program received signal SIGSEGV, Segmentation fault.
0x0000000000449672 in fit_command () at fit.c:1924
1924                err_data[num_data] = 1; /* constant weight */

(gdb) print num_data
$1 = 0
(gdb) print err_data
$2 = (double *) 0x0
((gdb) print max_data
$2 = 2048
(gdb) print num_errors
$4 = 0

So err_data is being allocated as length 0 because num_errors = 0.
But then it is accessed anyway.
What's the fix?

	Ethan