[mlir][bytecode] Fix external resource bytecode parsing (#97650)

The key was being dropped for external resources because they aren't
present in the dialect resource name mapper.

mlir/lib/Bytecode/Reader/BytecodeReader.cpp

@@ -706,7 +706,7 @@ LogicalResult ResourceSectionReader::initialize(
     auto resolveKey = [&](StringRef key) -> StringRef {
       auto it = dialectResourceHandleRenamingMap.find(key);
       if (it == dialectResourceHandleRenamingMap.end())
-        return "";
+        return key;
       return it->second;
     };