Fix Cycles fluid motion blur not working after recent refactor

This also re-enables the fluid motion blur test.

intern/cycles/blender/blender_mesh.cpp

@@ -965,6 +965,12 @@ void BlenderSync::sync_mesh_motion(BL::Depsgraph b_depsgraph,
                                    Mesh *mesh,
                                    int motion_step)
 {
+  /* Fluid motion blur already exported. */
+  BL::FluidDomainSettings b_fluid_domain = object_fluid_liquid_domain_find(b_ob);
+  if (b_fluid_domain) {
+    return;
+  }
+
   /* Skip if no vertices were exported. */
   size_t numverts = mesh->verts.size();
   if (numverts == 0) {

tests/python/modules/render_report.py

@@ -31,7 +31,7 @@ COLORS = COLORS_DUMMY
 
 # NOTE: Keep everything lowercase.
 BLACKLIST = (
-  'fluid_motion_blur.blend',
+  # 'file_to_blacklist.blend',
 )
 
 def print_message(message, type=None, status=''):