Fix segfault when '[]' used for row_vector_property. * graphics.in.h (row_vector_property::add_constraint (octave_idx_type len)): Remove validation that accepts 0x0 matrix. * graphics.in.h (image::init): Call add_constraint() to allow 0x0 since xdata, ydata can legitimately be '[]' for these properties.

EXTRA_DIST += \
  m4/module.mk \
  m4/ax_blas.m4 \
  m4/ax_blas_f77_func.m4 \
  m4/ax_compare_version.m4 \
  m4/ax_lapack.m4 \
  m4/ax_openmp.m4 \
  m4/ax_pthread.m4 \
  m4/gnulib-cache.m4 \
  m4/libtool.m4 \
  m4/ltoptions.m4 \
  m4/ltsugar.m4 \
  m4/ltversion.m4 \
  m4/lt~obsolete.m4 \
  m4/pkg.m4