[GREENFOOT-804] Class loading exception can prevent Greenfoot startup

If a class is missing in the initial scenario, Greenfoot may fail to load, due to failure to handle LinkageError's. As reported by user:

{code} Exception in thread "JavaFX Application Thread" java.lang.NoClassDefFoundError: Lovai at java.lang.Class.getDeclaredConstructors0(Native Method) at java.lang.Class.privateGetDeclaredConstructors(Class.java:2671) at java.lang.Class.getDeclaredConstructors(Class.java:2020) at bluej.utility.JavaReflective.getDeclaredConstructors(JavaReflective.java:364) at greenfoot.guifx.GreenfootStage.hasNoArgConstructor(GreenfootStage.java:1375) at greenfoot.guifx.GreenfootStage.showProject(GreenfootStage.java:478) at greenfoot.guifx.GreenfootStage.(GreenfootStage.java:395) at greenfoot.guifx.GreenfootStage.makeStage(GreenfootStage.java:597) {code}

(etc).

---

Issue metadata

• Issue type: Bug
• Priority: Medium
• Fix versions: 3.5.3