partially fix MIME type lookup by file extension

this is not particularly efficient but it's only used in local operation

src/main/java/com/conveyal/analysis/controllers/LocalFilesController.java

@@ -33,7 +33,9 @@ private Object getFile (Request req, Response res) throws Exception {
         FileStorageKey key = new FileStorageKey(category, filename);
         File file = fileStorage.getFile(key);
         FileStorageFormat format = FileStorageFormat.fromFilename(filename);
-        res.type(format.mimeType);
+        if (format != null) {
+            res.type(format.mimeType);
+        }
 
         // If the content-encoding is set to gzip, Spark automatically gzips the response. This double-gzips anything
         // that was already gzipped. Some of our files are already gzipped, and we rely on the the client browser to

src/main/java/com/conveyal/file/FileStorageFormat.java

@@ -1,5 +1,7 @@
 package com.conveyal.file;
 
+import java.util.Locale;
+
 /**
  * An enumeration of all the file types we handle as uploads, derived internal data, or work products.
  * Really this should be a union of several enumerated types (upload/internal/product) but Java does not allow this.
@@ -37,7 +39,12 @@ public enum FileStorageFormat {
     }
 
     public static FileStorageFormat fromFilename (String filename) {
-        String extension = filename.substring(filename.lastIndexOf(".") + 1);
-        return FileStorageFormat.valueOf(extension.toUpperCase());
+        String extension = filename.substring(filename.lastIndexOf(".") + 1).toLowerCase(Locale.ROOT);
+        for (FileStorageFormat format : FileStorageFormat.values()) {
+            if (format.extension.equals(extension)) {
+                return format;
+            }
+        }
+        return null;
     }
 }