fix(compartment-mapper): throw if policy/packagePolicy mismatch

The logic forbids it, but type inference doesn't necessarily--better to be safe.

packages/compartment-mapper/src/node-modules.js

@@ -612,6 +612,12 @@ const translateGraph = (
       policy,
     );
 
+    /* c8 ignore next */
+    if (policy && !packagePolicy) {
+      // this should never happen
+      throw new TypeError('Unexpectedly falsy package policy');
+    }
+
     /**
      * @param {string} dependencyName
      * @param {string} packageLocation