add checks to get_model and get_data

Author: TomDonoghue

fooof/objs/fit.py

@@ -626,6 +626,8 @@ def get_data(self, component='full', space='log'):
         With space set as 'linear', this combination holds in linear space.
         """
 
+        if not self.has_data:
+            raise NoDataError("No data available to fit, can not proceed.")
         assert space in ['linear', 'log'], "Input for 'space' invalid."
 
         if component == 'full':
@@ -671,6 +673,8 @@ def get_model(self, component='full', space='log'):
         With space set as 'linear', this combination holds in linear space.
         """
 
+        if not self.has_model:
+            raise NoModelError("No model fit results are available, can not proceed.")
         assert space in ['linear', 'log'], "Input for 'space' invalid."
 
         if component == 'full':