Fix handling of getting "modulemd: null" in MBS verbose response

The code made some half-hearted attemps to handle a MBS verbose query
missing the modulemd data, but it didn't do anything logically
consistent - fix it to consistently ignore such modules.

module_build_service/resolver/MBSResolver.py

@@ -144,18 +144,16 @@ class MBSResolver(KojiResolver):
         if not modules:
             return []
 
-        yaml = None
         mmds = []
         for module in modules:
-            if module:
-                yaml = module["modulemd"]
-
+            yaml = module["modulemd"]
             if not yaml:
                 if strict:
                     raise UnprocessableEntity(
                         "Failed to find modulemd entry in MBS for %r" % module)
                 else:
-                    return None
+                    log.warning("Failed to find modulemd entry in MBS for %r", module)
+                    continue
 
             mmds.append(load_mmd(yaml))
         return mmds
@@ -363,7 +361,10 @@ class MBSResolver(KojiResolver):
         else:
             queried_module = self.get_module(name, stream, version, context, strict=strict)
             yaml = queried_module["modulemd"]
-            queried_mmd = load_mmd(yaml)
+            if yaml:
+                queried_mmd = load_mmd(yaml)
+            else:
+                queried_mmd = None
 
         if not queried_mmd or "buildrequires" not in queried_mmd.get_xmd().get("mbs", {}):
             raise RuntimeError(