IVE: Crash on exporting

IV crashes when exporting a function with an nested function which name exists in the list of Imported Components.
Steps to reproduce:

• Open IVeditor
• Create a "Function 1" and add a nested "Function 2"
• Export "Function 1"
• Rename "Function 1" into "Function A"
• Export "Function A"
  -> 💥

Another crash happened during export (why?!?). It happened because sourceInterfaceGroup() in IVConnectionGroup::removeConnection returned a nullptr.