Add warning message when a linked variable doesn't exist

src/lib/decompositions.ts

@@ -959,6 +959,9 @@ function extractLinkedVariablesName(
   variableSummaryByName: VariableByName,
 ): void {
   const variableSummary = variableSummaryByName[name]
+  if (variableSummary === undefined) {
+    console.warn("Unknown variable in extractLinkedVariablesName():", name)
+  }
   for (const linkedVariableName of variableSummary?.linked_added_variables ??
     []) {
     if (!linkedVariablesName.has(linkedVariableName)) {