Handle 404 from CHS tide API without crashing or nuking stations

The CHS API sometimes returns 404 for station tide data requests.
Previously this raised an unhandled Mechanize::ResponseCodeError
through the entire Sinatra stack. Now we catch 404 specifically,
log a warning, and return nil — keeping the station in the list
so it can be retried on subsequent requests.

Author: jpr5

clients/chs_tides.rb

@@ -48,7 +48,15 @@ def tide_data_for(station, around)
 
             logger.info "getting tide data from #{url}"
 
-            return nil unless json = get_url(url)
+            begin
+                return nil unless json = get_url(url)
+            rescue Mechanize::ResponseCodeError => e
+                if e.response_code == "404"
+                    logger.warn "404 for station #{station.id}, skipping (may be temporary)"
+                    return nil
+                end
+                raise
+            end
 
             logger.debug "parsing tide predictions for #{station.id} from API #{API_URL}"
             data = JSON.parse(json) rescue []