Avoid returning a value when injected as content script

src/lib/diff/swatinem_diff.js

@@ -241,3 +241,23 @@
 
     return Diff;
 })(self);
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+/*******************************************************************************
+
+    DO NOT:
+    - Remove the following code
+    - Add code beyond the following code
+    Reason:
+    - https://github.com/gorhill/uBlock/pull/3721
+    - uBO never uses the return value from injected content scripts
+
+**/
+
+void 0;