Fix condition for resetting generated content
Fix condition for resetting generated content

The condition was removed in 56e45f9759e4fb1d0d0de0441ebbf55b22d5a3e4
under the assumption that there would be no `dompdf_generated` frames
with `content` set to `normal` or `none` anymore. But split-off
generated frames are set to `normal` with the intention of preventing
generated content from being added anew or being removed; the condition
ensures that the child frames of a split-off generated frame are not
being removed after a page break. Only a page break before the first
fragment is intended to reset generated content.

dompdf/dompdf,dompdf/dompdf