summary.py: minor fix in case par file contains no F1 value

cwinpy/pe/summary.py

@@ -906,7 +906,7 @@ def generate_summary_pages(**kwargs):
             if p["F0"] is not None:
                 f0s[psr] = p["F0"]
 
-            if p["F1"] is not None:
+            if len(p["F"]) > 1 and p["F1"] is not None:
                 fdots[psr] = p["F1"]
 
     # get table of upper limits