@Override
	public boolean isEnabledForContext(ListingActionContext context) {
		return getExternalSymbol(context) != null;
	}
Creates the action for editing an existing external location or external function in the 
listing.
@param plugin the label manager plugin, which owns this action.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/label/EditExternalLabelAction.java