[inferconfig] don't fail during filtering if a file does not exist

infer/src/backend/inferconfig.ml

@@ -95,11 +95,13 @@ module FileContainsStringMatcher = struct
           try
             DB.SourceFileMap.find source_file !source_map
           with Not_found ->
+              try
                 let file_in = open_in (DB.source_file_to_string source_file) in
                 let pattern_found = file_contains regexp file_in in
                 close_in file_in;
                 source_map := DB.SourceFileMap.add source_file pattern_found !source_map;
                 pattern_found
+              with Sys_error _ -> false
 end
 
 let filters_from_inferconfig inferconfig : filters =