[surface] Protect against the user setting a fallback resolution of 0.

Bug 23067 -- using clear drawing operator crashes printing
http://bugs.freedesktop.org/show_bug.cgi?id=23067

Here we were hitting an assert within the paginated surface after creating
a zero sized fallback image, due to the paginated surface being created
with an x fallback resolution of 0 dpi (by
_gtk_printer_create_cairo_surface(), gtk/gtkprinter.c:924).

Avoid the bug by guarding against bad input to
cairo_surface_set_fallback_resolution() which also allows us to identity
the invalid caller.

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