WS-601: fixing potential sites of UnboundLocalError

• fixed a couple potential (one actual) sites of UnboundLocalError
• turned a few magic strings into constants

apps/cli/executables/pexable/ingest_envoy/ingest_envoy/ingestion_manifest.py

@@ -69,7 +69,6 @@ class ManifestIF(ManifestComponentIF):
         self.telescope = telescope
 
         self.parameters = self.build_ingest_parameters(additional_metadata)
-
         self.files_found = [file for file in self.staging_source_dir.iterdir()]
 
     def build_ingest_parameters(self, additional_metadata: AbstractTextFile):
@@ -270,10 +269,14 @@ class IngestionManifestBuilder:
         # find science product (we expect just one for this SP type)
 
         tars_found = find_output_tars(self.files_found, self.staging_source_dir)
+
+        sci_prod = None
         for file in tars_found:
             sci_prod = OutputScienceProduct(type=self.sp_type, filename=file.name)
+            break
 
-        return OutputGroup(science_products=[sci_prod])
+        if sci_prod:
+            return OutputGroup(science_products=[sci_prod])
 
     def _build_imaging_output_group(self) -> OutputGroup:
         """