false extend/import cycle detected

[jurgenvinju]

Describe the bug

[ERROR] Users/jurgenv/git/rascal/src/org/rascalmpl/library/lang/box/util/Tree2Box.rsc:28:0: Code execution failed:
    [ERROR] |std:///ParseTree.rsc|(5736,12,<143,0>,<143,12>):143:0: Extend/import cycle detected:
    * |std:///ParseTree.rsc|
    * |std:///String.rsc|
    * |std:///List.rsc|
    Advice: |https://www.rascal-mpl.org/docs/Rascal/Errors/CompileTimeErrors/CyclicImportExtend|

This is on the rascal-formatter branch running mvn compile and during the tutor execution. While executing this on the commandline shell, I get the same error on:

import lang::box::\syntax::Box;

[jurgenvinju]

This is line 26-28 in Tree2Box:

@examples{
```rascal-shell
import lang::box::\syntax::Box;

[jurgenvinju]

This code in Import.java assumes that if an ununitialized module is detected, this means that an import/extend cycle is happening. However, in this case there is no cycle, and still an uninitialized module is on the stack.