empty start date secured (#1164)

Author: piotrmilcarz

lib/travis/api/v3/services/executions/for_owner_per_repo.rb

@@ -40,7 +40,7 @@ def recuce_by_repo(results) # rubocop:disable Metrics/AbcSize, Metrics/MethodLen
     end
 
     def calculate_minutes(start, finish)
-      return 0 if finish.to_s.empty?
+      return 0 if start.to_s.empty? || finish.to_s.empty?
 
       ((Time.parse(finish.to_s) - Time.parse(start.to_s)) / 60.to_f).ceil
     end

lib/travis/api/v3/services/executions/for_owner_per_sender.rb

@@ -39,7 +39,7 @@ def recuce_by_sender(results) # rubocop:disable Metrics/AbcSize, Metrics/MethodL
     end
 
     def calculate_minutes(start, finish)
-      return 0 if finish.to_s.empty?
+      return 0 if start.to_s.empty? || finish.to_s.empty?
 
       ((Time.parse(finish.to_s) - Time.parse(start.to_s)) / 60.to_f).ceil
     end