Don’t crash with Pango 1.42

Debian stable (Buster, 10) includes Pango 1.42. Until the next version of
Debian (Bullseye, 11) is released, keep a workaround to avoid crashes.

This workaround is not documented on purpose, support of Pango 1.42 will not be
improved. Also note that WeasyPrint with Pango 1.42 will suffer from #1199.

Fix #1384.

weasyprint/text/line_break.py

@@ -97,7 +97,12 @@ def setup(self, context, font_size, style):
         pango_context = ffi.gc(
             pango.pango_font_map_create_context(font_map),
             gobject.g_object_unref)
-        pango.pango_context_set_round_glyph_positions(pango_context, False)
+        try:
+            pango.pango_context_set_round_glyph_positions(pango_context, False)
+        except AttributeError:
+            # TODO: remove this when Cairo 1.44+ is in Debian 11 is released.
+            # See https://github.com/Kozea/WeasyPrint/issues/1384.
+            pass
         self.layout = ffi.gc(
             pango.pango_layout_new(pango_context),
             gobject.g_object_unref)