Fix AttributeError: 'Project' object has no attribute 'datafile_controller' (#3012)

- Add datafile_controller property to Project class that returns self.controller
- Add null checks in _ImportSuggester to handle when datafile_controller is None

This fixes the crash when using Library Finder on a clean install without an open project.

Closes #2989

Author: chelslava

src/robotide/controller/project.py

@@ -152,6 +152,10 @@ def data(self):
     def suite(self):
         return self.controller.data if self.controller else None
 
+    @property
+    def datafile_controller(self):
+        return self.controller
+
     @property
     def datafiles(self):
         return self._suites() + self.resources

src/robotide/namespace/suggesters.py

@@ -110,12 +110,16 @@ def __init__(self, controller):
 
     def get_suggestions(self, name, *args):
         _ = args
+        if self._df_controller is None:
+            return []
         already_imported = self.get_already_imported()
         all_resources = self.get_all_available()
         suggestion_names = all_resources - already_imported
         return [self._suggestion(n) for n in sorted(suggestion_names) if name in n]
 
     def get_already_imported(self):
+        if self._df_controller is None:
+            return set()
         return set(imp.name for imp in self._df_controller.imports)
 
     def get_all_available(self):