fix accessWithInit helper function

lib/library/AssignLibraryPlugin.js

@@ -29,21 +29,43 @@ const accessWithInit = (accessor, existingLength, initLast = false) => {
 	// This generates for [a, b, c, d]:
 	// (((a = typeof a === "undefined" ? {} : a).b = a.b || {}).c = a.b.c || {}).d
 	const base = accessor[0];
+	if (accessor.length === 1 && !initLast) return base;
 	let current =
-		existingLength > 0 || (!initLast && accessor.length === 1)
+		existingLength > 0
 			? base
 			: `(${base} = typeof ${base} === "undefined" ? {} : ${base})`;
-	let propsSoFar = accessor.slice(1, existingLength);
-	current += propertyAccess(propsSoFar);
-	if (existingLength >= accessor.length - 1) return current;
-	for (let i = Math.max(1, existingLength); i < accessor.length - 1; i++) {
+
+	// i is the current position in accessor that has been printed
+	let i = 1;
+
+	// all properties printed so far (excluding base)
+	let propsSoFar;
+
+	// if there is existingLength, print all properties until this position as property access
+	if (existingLength > i) {
+		propsSoFar = accessor.slice(1, existingLength);
+		i = existingLength;
+		current += propertyAccess(propsSoFar);
+	} else {
+		propsSoFar = [];
+	}
+
+	// all remainig properties (except the last one when initLast is not set)
+	// should be printed as initializer
+	const initUntil = initLast ? accessor.length : accessor.length - 1;
+	for (; i < initUntil; i++) {
 		const prop = accessor[i];
 		propsSoFar.push(prop);
 		current = `(${current}${propertyAccess([prop])} = ${base}${propertyAccess(
 			propsSoFar
 		)} || {})`;
 	}
-	return `${current}${propertyAccess([accessor[accessor.length - 1]])}`;
+
+	// print the last property as property access if not yet printed
+	if (i < accessor.length)
+		current = `${current}${propertyAccess([accessor[accessor.length - 1]])}`;
+
+	return current;
 };
 
 /**