SL: Minor fixes.

src/Model/SedimentLayer/SedimentLayer.py

@@ -143,7 +143,12 @@ class SedimentLayer(SQLSubModel):
         SedimentLayer._id_cnt = max(id, SedimentLayer._id_cnt+1)
 
     def __str__(self):
-        return f"{self.name} ({len(self)}) - {self.comment}"
+        s = f"{self.name} ({len(self)})"
+
+        if self.comment != "":
+            s += f" - {self.comment}"
+
+        return s
 
     def __len__(self):
         return len(self._layers)

src/View/SedimentLayers/Reach/SLDialog.py

@@ -46,6 +46,9 @@ class SLDialog(ASubWindow, ListedSubWindow):
 
     @property
     def sl(self):
+        if self.value == _translate("SedimentLayers", "Not defined"):
+            return None
+
         return next(
             filter(
                 lambda sl: str(sl) == self.value,