layers: Fix script crash for special-cased err enum

Change-Id: Ic054c35fd777e66e85ed56978ad1628ec24b94a6
diff --git a/layers/vk_validation_stats.py b/layers/vk_validation_stats.py
index a586f67..18ff01b 100755
--- a/layers/vk_validation_stats.py
+++ b/layers/vk_validation_stats.py
@@ -170,6 +170,7 @@
         # 1790 is a special case that provides an exception when an extension is enabled. No specific error is flagged, but the exception is handled so add it here
         self.enum_count_dict['VALIDATION_ERROR_1500099c'] = {}
         self.enum_count_dict['VALIDATION_ERROR_1500099c']['count'] = 1
+        self.enum_count_dict['VALIDATION_ERROR_1500099c']['file_line'] = []
     def parse(self):
         duplicate_checks = 0
         for sf in self.source_files: