Do not throw error when settings are inconsistent

We store settings at various level in the IDE (module, project, app), and those settings are persisted on disk. It could happen that some of those files are deleted on disk for any reason, and the settings would become inconsistent (e.g. a binding override is defined on a module but the project is not bound). We check consistency at creation time in the settings UI, but we can't be sure later the settings will remain coherent.

In this case we should not throw errors such as: 

java.lang.NullPointerException at java.base/java.util.Objects.requireNonNull(Objects.java:221) at org.sonarlint.intellij.core.ModuleBindingManager.getEngineIfStarted(ModuleBindingManager.java:145) at org.sonarlint.intellij.module.ModuleChangeListenerKt.getEngineIfStarted(ModuleChangeListener.kt:35) at org.sonarlint.intellij.module.ModuleChangeListenerKt.access$getEngineIfStarted(ModuleChangeListener.kt:1) at org.sonarlint.intellij.module.ModuleChangeListener.moduleAdded(ModuleChangeListener.kt:39)