Fix zero spin conversion

This fixes the issue in #588 (closed). It just needed some rearranging of the order in which the various parameters are added and calculation are performed when filling in the missing pieces of the result object.

bilby/gw/conversion.py

@@ -782,7 +782,6 @@ def _generate_all_cbc_parameters(sample, defaults, base_conversion,
             logger.debug('Assuming {} = {}'.format(key, default))
 
     output_sample = fill_from_fixed_priors(output_sample, priors)
-    output_sample, _ = base_conversion(output_sample)
     if likelihood is not None:
         if (
                 hasattr(likelihood, 'phase_marginalization') or
@@ -819,6 +818,9 @@ def _generate_all_cbc_parameters(sample, defaults, base_conversion,
                     "Failed to generate sky frame parameters for type {}"
                     .format(type(output_sample))
                 )
+    if likelihood is not None:
+        compute_snrs(output_sample, likelihood)
+    output_sample, _ = base_conversion(output_sample)
     for key, func in zip(["mass", "spin", "source frame"], [
             generate_mass_parameters, generate_spin_parameters,
             generate_source_frame_parameters]):
@@ -828,8 +830,6 @@ def _generate_all_cbc_parameters(sample, defaults, base_conversion,
             logger.info(
                 "Generation of {} parameters failed with message {}".format(
                     key, e))
-    if likelihood is not None:
-        compute_snrs(output_sample, likelihood)
     return output_sample
 
 
@@ -1154,7 +1154,6 @@ def compute_snrs(sample, likelihood):
             matched_filter_snrs = {
                 ifo.name: [] for ifo in likelihood.interferometers}
             optimal_snrs = {ifo.name: [] for ifo in likelihood.interferometers}
-
             for ii in tqdm(range(len(sample)), file=sys.stdout):
                 signal_polarizations =\
                     likelihood.waveform_generator.frequency_domain_strain(